for some reason this was removed by a mod on ml with no indication as to why it was removed...

Because AskLemmy is for open ended discussion, not for tech support or meta discussions about Lemmy's development.

Doesn't all that take place on the Git platform?

Doesn't make sense to have those discussions here when GitHub/lab/tea wherever it is hosted has a discussions area.

Don't take it too hard on yourself, but asklemmy isn't the place to ask for tech support, which is likely why your post was removed on .ml

better places would be on !lemmy@lemmy.ml, lemmy support communities, selfhosted, etc. You should use those support communities even if there hasn't been activity in a while.

The issue is there are several ways of installing Lemmy and the way to upgrade each type may be different. I suppose no one has written documentation on the update process. Best place to have it may be on the join-lemmy.org site through a pull request. Or if that's too much work there should be a community for lemmy mods and admins that want to share their experiences and ask questions.

Isn't there !lemmy_support@lemmy.ml for this kind of questions?

Wouldn't it make more sense to be asking this in one of the meta / tech focused lemmunities?

The selfhosted community is a bit more active, but also very few admins actually use exactly the provided Ansible stuff, if at all. My distro isn't even supported by it, mine's just a hand written podman-compose. All of the bigger instances are running in the cloud, Kubernetes or otherwise. Some people don't use Docker at all. There's AUR packages for ArchLinux to run it directly.

As a result, each problem one might encounter is different and often they run into different types of problems, none of which are about how to get the new Lemmy version running but rather tweaking and cleaning up the database, moving pict-rs to object storage, etc.

You should go learn Ansible and Docker and actually understand what it does and how to customize it for your own needs. There won't always be someone around to spoonfeed you the answers. Ansible on its own is already made to be super simple so that any random sysadmin can pick it up with zero programming knowledge.

It doesn’t give any details to where I might find the vars.yml file

I don't run a Lemmy instance, but if you have locate installed on your Linux system, you probably have a cron job that periodically updates the database that locate uses. You can probably just type locate vars.yml.

If you don't, and don't want to have locate installed, I suppose you can always run find / -name vars.yml, though it'll take a bit.