Disagree.
There is NO error situation, as the App is there and working, it’s just not configured. Not the same.
Second: Installing an App silently with an update of NC without guiding through a configuration process or providing any information about the App being installed, what it is and that it needs Docker and a configuation is a NoGo and not only unprofessional but also very bad UX.
So you’d prefer a yellow warning sign then? 
Yep, I agree, and I never said otherwise in any of my previous posts.
EDIT:
Small addition:
I’d go even further and say that installing an app silently when you know that many of your users don’t need it and, even worse, can’t use it because Docker is kind of difficult to set up, let’s say, in a web hosting environment , is unprofessional.
On the other hand, so called “professional” products would likely bothering you with messages like `Did you already try our AppAPI?’ Expand your experience with our new AppAPI’, and maybe even spam the notification area, or worse, using full screen pop-ups when logging in. Not sure if that would have been received better here.
Anyways, my point was: Yeah, not cool. But there’s no need to bring out the big guns and talk about ‘enshitification’ because of something like this.
Reading through the thread, the answer the OP was looking for hasn’t been given. The simple answer is, that if you don’t need the AppAPI (and a lot of people probably won’t), then you can just go to Active Apps and disable it.
As to why it was turned on by default is another matter.
Personally, I feel that it shouldn’t have been, all it is doing is annoying users who don’t need that function and is driving ordinary people away from Nextcloud.
If Nextcloud really wants to gain traction, it HAS to stop driving away ordinary people who just want to escape from Big Tech. Not all of us want to make out that we are super techy sys admins, we just want stuff that works and can make our lives better without having to use the “services” of the big spyware companies.
Not true.
Well, but the world isn’t always as simple as we would like it to be, is it?
In my opinion, that’s the only “matter” here. Because if it weren’t automatically enabled, no error message would have popped up, and this thread almost certainly wouldn’t exist.
I think it already has gaind quite a lot of traction,
See, this is the argument I never really understand whenever it comes up here. Of course, things can always be optimised and improved, but that doesn’t change the fact that if you’re installing server apps — whether it’s on a home server/NAS, or with a web hosting provider like the OP — then you’re no longer a ‘regular user’. You’re part of a very small group, maybe 1% of users at most. Normal users don’t have a home NAS and for sure they don’t provide any server apps in any form or fashion, regardless of how “easy” it might get. They might install an app from the Play Store or Apple App Store, but for most of them, that’s where their administrative interaction with computers ends!
Nevertheless, self-hosting has generally become much easier; otherwise, I would argue that many people here (including myself) would not be able to host their own Nextcloud server. However, it still requires you to consult the documentation from time to time, as well as perhaps using your preferred search engine or a forum to find answers to specific questions. If you call that beeing a ‘super techy sys admin’, then I suppose we’re all super techy sys admins!
By the way, the AppAPI isn’t just about AI. It allows app developers to build Nextcloud apps in programming languages other than PHP and integrate them in a standardised way. This helps to attract a broader developer base.
I made an account here just to reply to this thread.
Unlike some / most (?) of the users in this thread, I’m a Sysadmin by trade.
I just upgraded NC from 31 to 32 and got this warning, same as OP.
First, I searched DDG and didn’t see anything specifically referring to the warning. Next thing I did was check the upgrade notes because previous new-to-me setup warnings were usually noted: Upgrade to Nextcloud 32 — Nextcloud latest Administration Manual latest documentation
There is no mention of “AppAPI” in the notes. No explanation of the critical “error” that I got on the setup warnings page, no explanation of what AppAPI is, whether I would need it or not.
As someone mentioned, the docs to explain how to set up a container for it, but, like much documentation I find, it’s missing the why.
(it also doesn’t seem to explain what HaRP is or what it stands for, it dives straight into setting it up)
A lot of that is answered here, but for something like this it should be in the upgrade notes!
It could be as simple as:
Upon upgrading to NextCloud 32, the AppAPI extension is installed and enabled. This allows external applications to run in a Docker container and communicate with NextCloud. This needs a some configuration to set up. If you don’t need it, you can disable the extension to remove the warning. To read more, see AppAPIAndExternalApps.html
To be fair, the error message refers to the settings…
…and there it says:
AppAPI
The AppAPI Project is an exciting initiative that aims to revolutionize the way applications are developed for Nextcloud through the use of docker containers. Allowing for greater programming language choice and allowing computationally expensive tasks to be offloaded to a different server.
But yes, I agree that this could have been handled better. I think it should never have been enabled by default. And if they insist on doing so, there should at least be links to explanations and documentation in the error message itself.
However, I also understand that they want to make users aware of new features and possibilities, so they should probably come up with a better way of doing this in the medium term. I would suggest adding a ‘News’ section to the ‘Overview’ page, or something similar.
So, as i understood correctly that “exciting initiative”, they are going to force us to install docker directly onto the production server. And if my security department says no to docker on the same nextcloud server, it is nextcloud who will be ditched, not our security department. So, yes, this is the first sign to start looking for more secure and industrialized alternatives.
And how does one do that?
In the same way that you would disable any other app. Log in to your Nextcloud account as an administrator, go to the ‘Apps’ page, then select ‘Active Apps’. Find the ‘AppAPI’ app in the list and click ‘Disable’.
I was looking in the administrator settings, but it turns out to be another menu.
Thank you!