Should Trump show up for CNN's "invitation"?

No.

Should he (and Harris) be willing to debate on any reasonable schedule and number of times?  Yes.

So how do you square these two?  Simple -- the current format as presented are not debates.

We can't leave aside the affidavit that exists on the ABC "debate" and the allegedly-deliberate gaming of it along with the complaint filed with the SEC related to same since Disney, which is a public company and owns ABC.  The root of the problem however is not whether or not such occurred: It is that the deliberate structure of these events has been designed in the last couple of decades so such games can occur, and thus they're not DEBATES.

How else do you explain the fact that Fox News offered both candidates a debate immediately when Harris deposed Biden and she has yet to answer but the media calls Trump a "coward" for refusing to "debate" on CNN after it is disclosed and quite-clear, simply from the stagecraft, that ABC got in the middle of the one they hosted even if only with the height of the lecterns.

Simply put what the media proposes are stage shows, not debates.  They're no more "real" than a WWE "wrestling" match.

If you've ever actually done debating (e.g. in High School, if you attended a real one, or College if you actually got a rigorous education in same) you understand this.  An actual debate is on a subject or set of subjects agreed to by both parties in advance.  Both parties comes and present their case in an opening statement, there are frequently some set of questions which must be related to the subjects under debate and the persons asking them should be selected by the adversary of each side, there is a limited time for answer to each question and then finally a summation.

Note that the moderator has no role in asking anything; the only questions from the floor are from a limited number of adversaries chosen by the other side and limited in both scope and number.  This prevents anyone from tampering with either the words or tone of the question as they don't have it in advance.  Each candidate is permitted a pen and paper for notes and any pre-arranged notes on cards or similar that they wish (along with the displays for the main presentation) but no communication devices of any sort.

I would agree to any number of debates and would urge both sides to do so under the following conditions:

• There is no preference in lighting, audio or lectern; the choice of lectern is determined once both candidates show up and make a coin toss.
  
  
• The topics to be debated are limited to one or two per debate and fully disclosed at least a week in advance to each side.  No topic beyond the subjects of the debate will be entertained.
  
  
• Each side gets a 3 minute opening statement; no written material or charts are permitted, words only.  Flip a coin for who goes first (and that will determine the closing statement order in reverse.)
  
  
• Next each side gets a 15 minute uninterrupted period to make their case with whoever won the coin toss going first.  They may present written charts, data or other materials but those must be publicly displayed so the audience and the other party can see them and are part of the permanent record.  No interruptions are permitted from the other side during this time.
  
  
• 5 minute Intermission.  Go pee if you need to.
   
• Each side now gets two challengers, chosen by their opponent and not necessarily disclosed until the time of the debate, that stand and ask one or more questions on the presentation.  The questions must bear on the topics of the debate and the challenger is permitted two minutes to ask said question(s), which must be complete before the answer period begins, with each response by the candidate being no more than five minutes in length.  The challengers alternate (flip a coin as to who goes first) until exhausted and the other side must stand mute during that time.
  
  
• Once exhausted each candidate has five minutes of rebuttal related to the questions and answers.  Again, uninterrupted but the rebuttals must pertain to the topics, presentations, questions and answers.  Anything within that scope is fair game.
  
  
• After the rebuttal each person gets a five minute uninterrupted closing statement.  The person who lost the opening coin toss has the option to go first or last as they prefer and he or she makes such election after the questions and rebuttals are exhausted.

This will run right near 90 minutes total.  Some people would argue that they want more but I'm deliberately limiting to the topics to two per debate and there will be more than one debate, allowing the subject matter at hand to be expanded upon and explained.  Open door topic areas can't be done in this amount of time and longer periods of time simply exceed Americans' willingness to listen and networks' willingness to block the time for it.  In addition the terms must require that simulcast to other networks and unlimited and no-fee video access must be permitted, whether by the principal agency or anyone else who wishes to; each such presentation must explicitly waive all copyright and other related claims.

The moderator has no questioning authority whatsoever.  His or her job is only to present the candidates and be the host of the proceedings.  If one of the parties wishes to assert that the other has lied that is the purpose of rebuttal or closing statement period.  The moderator's only job is to mute a microphone if either presenter runs out of time and refuses to cease or if they attempt to go outside the topics of the debate.  The microphones are directional (super-cardioid pattern) with the lecterns placed at a roughly 20 degree off-axis angle to center so as to make attempting to shout over or otherwise interrupt non-productive (each candidate is in the side-lobe "null" of the other's microphone) and each mic is only enabled when it is the candidate's turn to speak.  The standard 3-light tree is to be present on each lectern with a countdown timer (green > 2 minutes remaining on the displayed clock, yellow < 2 minutes, red time has expired and microphone is OFF) and a prominently-displayed and large "straight ahead" countdown clock directly in the sightline of each candidate at the back of the room corresponding to the lights on the lectern.

I would argue these should be presented before a live audience with the proviso that no interruptions from said audience is permitted, and if you violate that you get removed from the room -- and during that period of time the person who has the floor has their time suspended.  I like the presence of an audience but a "heckler's veto" must be prohibited and evenly enforced.  If that cannot be reasonably assured then no audience it is.

That's it.

The premise that a "news organization" can play "gotcha" and favor one side or the other makes any such "debate" nothing more than a stage show.  Either let us see real debates or stop the charade.