@Zergling_man

I do not know what you mean

I do not know what a client is

@shortstories A server is something that waits for connections to be made, and does stuff in response to that. A client is something that makes a connection.
A web browser, in other words, is an HTTP client. (And nginx, for example, is an HTTP server.)
A "web front-end" is a javascript-based client, generally for the server it's fetched from (but see, eg. bloat.freespeechextremist.com for exceptions). In this case, that is what I am referring to by "web client". By "some other client" I am talking about things like tut, thedesk*, subwaytooter, whatever. Those three are the ones I generally recommend.

*thedesk is actually written in javascript, and runs on electron, so you could argue that it is still a "web client". The key difference is that the code lives on your computer, instead of a remote server, and it is thus significantly harder to alter without your consent.

@Zergling_man

If the client is on my computer then I do not see how the admin can fix that

What if I just need a new computer of the right type running the right browser

And the admin updating things won't fix stuff because my stuff is too old

@shortstories >If the client is on my computer then I do not see how the admin can fix that
If you're using a web client, that is, whatever's provided at https://merovingian.club/, then you're downloading it every time you go there (approximately), and it's living in temporary folders on your computer. If admin changes what's there, then next time you fetch it you're getting something different.

>What if I just need a new computer of the right type running the right browser
I'm taking this opportunity to announce my new service, Computr, which entirely solves the dependency problem. Simply write the name of a package on a postcard, staple it to about $300, and mail it to me. Within a week, a brand new computer will show up on your doorstep with only that package installed. If you do that for every program you ever need to run for the rest of your life then you'll never hit another dependency conflict again.
- https://michael.orlitzky.com/articles/motherfuckers_need_package_management.xhtml

>And the admin updating things won't fix stuff because my stuff is too old
It is entirely possible that javascript implementations on different (versions of) browsers results in different behaviour of the same scripts. This is why I can't login on seek.com after they changed to a "passwordless" login system, for example. But that's unlikely to result in the behaviour you're seeing here, given that editing a post is almost identical to creating a post. (IIRC it uses PATCH instead of POST so that MIGHT be relevant, but I think you also use PATCH to update your profile so if you can do that, you should be able to edit. And anyway, if it were that, you'd still have the edit button and be able to try, and then it would just silently - or maybe loudly - fail.)

To clarify, the problem is, as I understand it, in the scripts provided by your instance: They don't come with an edit button, they don't come with that functionality. That's why I recommend testing it on some other client, if the function does work on the instance directly, then the issue must be there.
If I'm wrong about that, and you actually do have such a button and it doesn't work, that's something you can chase directly by inspecting error logs.