Older wikis if you go Special:AdminDashboard have "Wiki Features" in the first "Wiki" row preceding the "Community" row, but if you visit the dashboard of newly created wikis you manage then it doesn't have a 'Wiki Features' button.
Furthermore when you click edit there's always this blue loading bar which lags for 1-2 seconds which is kind of annoying to wait for every time.
Old style editor doesn't lag like that, how can I revert to using the old-style non-laggy screen on these new wikis?
Also no 'add features and media' on right to easily add stuff. "Source Editor" on new wikis does have an image icon next to the link icon which allows uploading but it works very very slowly and it is hard to make rapid contributions this way.
The only fast way I can figure is to upload 1 image, manually insert gallery tags, and then add things to the gallery, because additions to existing galleries seem to be added in fewer steps than the standalone image uploading icon.
Got some insight at Thread:1851588 in May but could not bump due to 60 days passing.
I think maybe I want to be able to use forked 1.19 instead of 1.33 per Tupka's mention? But Andrew said it's not possible to switch back.
That also might answer my question of what UCP stands for...
This rigidity makes me wonder, are old wikis going to be eventually forced to use this laggy new editor? It's very pretty but perhaps it is aimed at high-speed comps/connections that make it load instantaneously? Still lags on 8GB RAM and 50Mbit download though, what specs are needed to axe this delay?
There are many blogs and threads describing what UCP is, why it is needed, and what changes are happening as a result. There is a summary help page at Help:Unified Community Platform and an unofficial list of known bugs at User:Noreplyz/UCP. The Zendesk help article you linked to contains a list of most of the relevant blogs/threads. It seems like you have already read through some of them. That Zendesk help article does not list blogs regarding the user database merge. If you want to know more of that, take a look at MisterWoodhouse's blogs. I believe he is the one that wrote all of the blogs regarding the database merger.
Fandom has implemented many custom features over the years. While these custom features have made things easy for users, it has been a maintainance nighmare for Fandom. They have been unable to upgrade MediaWiki beacuse of all the custom code they have that breaks when changing MediaWiki versions. Thus, the custom features are kept but new/improved features from MediaWiki's core don't get added. Fandom finally made the decision to bite the bullet and sacrifice the custom features in order to get a fresh start. Moving to a new version of MediaWiki means a lot of new/improved native features but it also means the loss of most custom features. Fandom is trying to reinvent some custom features but they will not be the same.
The admin dashboard and wiki features are two such custom features. I am not admin on a UCP wiki but I am told that the functionality of wiki features has been combined with admin dashboard. As for the editor, the classic editor that exists on non-UCP wikis is part of the MediaWiki core. The new version of MediaWiki used for UCP has a different editor. That is why you can't "switch back" to the old editor. As for adding meadia, the option should be in the editor's top bar.
All wikis will be converted to UCP. Fandom initially started by forcing its use via the creation process. However, since then, Fandom has started to convert non-UCP wikis to UCP as "comparable functionality" becomes available. At this time, only the most basic wikis have been moved. However, eventially, all wikis will be converted with absolutely no wikis remaining on the non-UCP platform.