Only Fandom can change that and it's only done when there is a large problem with vandalism. Preventing editors from being able to edit isn't what the platform is for.
It's probably a caching issue- try checking your preferences for a more exact count, bypassing the cache, or just waiting for it to update.
You can do it using CSS if you want custom colors or through this pre-made stylesheet for some automatic ones.
The .theme-fandomdesktop-light and .theme-fandomdesktop-dark CSS classes can be used to determine which styles to apply to an item for which theme.
The options you can use for Fandom wikis are in this section. If you want to disable it for every gallery on the site (and you're an admin there), you can use the CSS solution suggested by Muchos.
However, if you want to disable it on only certain galleries, you can use the "bordersize=none" parameter
Try submitting another ticket (or check your email for a response to the first one)
It's possible to do it with DPL (with the "include" set of parameters iirc), but an easier way for quick maintenance is through Special:TagsReport. You just need to input the template and parameter names and it will show all pages with them.
It changes the background color of the bar that appears on the top of the page once you scroll down. If you're looking at the bar after changing it and it's not changing, you might need to bypass your cache.
The survey showing up multiple times is a bug which should be fixed soon.
June 14, 2022: Issues loading Fandom has a report on what happened. The majority of issues were fixed but it seems like there's still a few left.
Fandom-original wikis use a custom gallery extension that doesn't support those modes. Fandom originally wanted to have all wikis use the standard MediaWiki gallery with the FandomDesktop migration, but it was reverted due to some complaints. If you want to switch your wiki to them, you can send in a ticket and they should be able to do it.
See Help:Navigation - it has a guide on how to configure the navbar
The one rename limit is supposed to make you actually chose a name you want to keep, instead of just making a bunch you don't actually want to keep. (and users would probably just blow through any additional renames before complaining that they have only 1 left)
You can try contacting Fandom and asking for a manual rename, but it's highly unlikely to happen. The other alternative is just making a new account.
For Twitter, Facebook, and Discord you just need to put the username (you can see from the URL that it's trying to go to https://twitter.com/twitter.com/username)
You can submit a ticket to Fandom staff to set the system message:
So for admin, you would ask them to change MediaWiki:Userprofile-global-tag-sysop to "Watcher" (though you probably shouldn't use a name like that as it can be confusing for users)