Pickysaurus

Based on the message, you need to create the folder at: C:\SteamLibrary\steamapps\common\Octopath_Traveler2\Octopath_Traveler2\Content\Paks\~mods
For help with the extension, you can contact the developer here: https://www.nexusmods.com/site/mods/166
It's very likely the developer of the extension is not properly checking that the folder exists (and creating it if it is missing). 

The downgrader for FOLON should be downloaded manually and run. It's not a Vortex compatible file 

Looks like the website is dead, but the GitHub page is still active https://github.com/CadeEvs/FrostyToolsuite/releases/

We cannot replicate the crash you describe. It has to be caused by something borked up in your setup. More information in this thread: 
 

Any kind of weird flickering can often be caused by your GPU acceleration settings. Try turning off GPU acceleration in the Vortex settings. 

Sounds like you may have moved the app data folder to G:\ at one point. 
You would need to tell Windows to look for it on C:\ again but exactly how I'm not sure

Did you restart Vortex after adding them? 
You're better off adding the files in the actual UI rather than manipulation of the folders.
There's a zone to drop archives at the bottom of the mods table

Try reinstalling Origin/EA Play? 
Alternatively you can look for your old Origin manifest files and delete them. Advice on that is here: https://modding.wiki/en/vortex/developer/game-detection#originea-play

The errors are caused by your PC (or something in your network connection) preventing the extension from being downloaded from GitHub. You can download and install it manually here https://www.nexusmods.com/site/mods/875
 
Make sure you install it in the "Extensions" section of Vortex rather than in the "Mods" section.

I'm afraid so. Profiles are gone forever if they get deleted. The mods should still be in Vortex though, just not enabled on your default profile. 

No, Vortex is intended to be used on a clean game install. 

This is almost certainly caused by a broken .NET 6 install. See this post:
 

Honestly it sounds like this is problem with how MO2 stores mods/games being incompatible with the importer. You can still do this manually as I mentioned before.

https://help.nexusmods.com/article/92-im-having-download-issues-what-can-i-do

This is a duplicate of this thread.
 
 

Please see the solution from the pinned thread here:
https://github.com/Nexus-Mods/Vortex/wiki/MODDINGWIKI-Users-Troubleshooting-NET-6-Install-Issues

I have no idea how you got into this state. Vortexposer's suggestion of two lists getting merged sounds plausible. 
There's no harm in them being there from a technical perspective. 
You might want to check the actual files which are at:
%appdata%\Vortex\fallout4\userlist.yaml %appdata%\Vortex\skyrimse\userlist.yaml If the rules exist in both files, it's safe to remove them from the UI in Fallout 4 without impacting Skyrim's list

This is a problem in your setup. See the post below for more
https://forums.nexusmods.com/topic/13483143-vortex-keeps-purging-when-i-download-and-install-a-mod/?do=getNewComment

Try this pinned solution:
 

This is covered in the pinned post: 
 

This error is caused by a third-party extension you've installed. Go to %appdata%\Vortex\plugins and delete any recently added game extensions. The last time this came up it was Battlefleet Gothic Armada 2 causing the problem. 

Vortex supports around 250-300 games, but it doesn't support every single game on the website. I suspect nobody has made an extension for the Mafia series yet. 

The game plugins are not managed by Vortex, they are managed by the game.

Something on your PC must be wiping the AppData folder - this doesn't ever happen the way Vortex works normally. 
 
Edit: The only possible way for this to have happened is if you put your mod staging folder inside your Vortex install folder. Vortex will try and prevent you from doing this. Did you install Vortex to a location outside of Progam Files? Where was your staging folder located? 

You can manually download the extension here: https://www.nexusmods.com/site/mods/196