Seek your opinions and knowledge about my planned itinerary for April 2027

actually Munich - Prague - Vienna - Salzburg is a logical circular tour and is the only sensible AI generated itinery I've seen this year!. It's the rest that seems to have been created by throwing darts at a map on the wall!!

Problems number 1 and 2: EES for Schengen area (plus possibly ETIAS by that date) and ETA for UK. That sequence has you queue up for EES entry checks at Paris then some days later queue up for the exit checks, whilst making sure you paid for ETA in advance before entering UK. Then some days later you queue up for EES all over again!! Now it's possible that EES delays will have been eliminated by then - but it's also possible that the ETIAS system will have come on line with more delays. It would be simpler to start in London and only enter the Schengen zone once, which would also save you the cost of one crossing of the English Channel.

The list as a whole looks like you are scared of leaving big cities. Or you think that each country only has a a few big cities and nothing in between. In reality you could spend all of your time in the London-Paris-Amsterdam triangle and still miss things. The Amsterdam-Munich transfer could fill at least two weeks. And the Munich-Prague-Vienna-Salzburg loop could fill more time than you have. Switzerland is a country, and your plan will give it a few days, little of which you will remember because of the rushed nature of the tour.

So calm down, and think about spending less time on transfers and more time actually soaking up the places you visit.

It's a bit difficult to comment without knowing what you are trying to optimize or see
with this itinerary.

It's not the most efficient, and you don't say how you plan to go between each city.
Paris to London and then back to Amsterdam is probably 2 half days of travel,
for example, whether you fly or take the train.

Also, I think you probably have too many places to cover in 23 days. If you are
counting arrival and departure days in that number, you actually have 21-23 full days
of travel, and 8 places (maybe more, since Switzerland has a lot of places). That
comes out to 2.5-3 days per place, not including travel time. You may want to
dive into detailed transport options to see how much time you would have in
each place.

You'll find many threads about the wisdom of using AI to plan a travel itinerary. It may
be helpful, but I wouldn't trust it completely, and I don't know how specific and detailed
you were in your phrasing of the question(s) you asked it.

Brigitte,
The above comments are worth paying attention to. The itinerary has too much doubling back on it. With (probably) 21-23 days, it would be best to fly into London first, then go to Paris or Amsterdam from there, and onward. Here is (just) my suggestion.
Starting with London, counting nights in a place (2 nights=one full day):
Day 1...Arrive London (sleep London)
Day2-3 London (sleep London)
Day 4 move to Amsterdam (Sleep Amsterdam)
Day5-6 Amsterdam (Sleep Amsterdam)
Day7 move to Paris(Sleep Paris)
Day8-10 Paris (Sleep Paris)
Day11 move to Prague (Sleep Prague)
Day12-13 Prague (Sleep Prague)
Day14 move to Vienna (Sleep Vienna)
Day15-16 Vienna (Sleep Vienna)
Day 17 move to Salzburg (Sleep Salzburg)
Day 18 Salzburg (Sleep Salzburg)
Day 19 move to Munich (Sleep Munich)
Days20-21 Munich (Sleep Munich)
Day 22 Fly home from Munich

This gives you: London 2 1/2 days, Amsterdam 2 1/2 days, Paris 3 1/2 days, Prague 2 1/2 days, Vienna 2 1/2 days, Salzburg 1 1/2 days, Munich 2 1/2 days. Each change of location will take a half day (or more, depending on mode of travel, time of day, etc.), hence the half days (travel and arrival days). You could add or subtract a day from one city or another.
With the amount of time you have, you may want to consider dropping one or more destinations altogether, to spend longer in a place. That is up to you and what you want to see and do in each city. There is no right or wrong way to do this trip. Just be aware that each move takes up more time from your trip than AI might calculate. Once you figure in these practicalities you might want to make adjustments. Each place you are going has so much to experience there that you may not want to shortchange it. Or this may be an introductory trip to whet your appetite for future travel. Whatever you decide on, have lots of fun and amusez-vous bien!

Seven countries in 25 days will be a lot of time in transportation and not much time for the best part of a European vacation- being out enjoying it. I am very stingy with my vacation time and don’t want train rides longer than two hours. And flying between cities will eat up a whole day, even if the flight is only 1-2 hours. Assume you will return to Europe and pare down what’s your actual priorities. There’s so much in each of those countries beyond a major city, too. Help us help you by sharing more about what are your goals for this trip, and we can give you better information.