thatcasualgamingguy
If I understand it correctly, the passwords are stored encrypted, but not the additional data, like website-URLs and app-names. This way the password manager only needs to temporarily decrypt a specific password when it’s needed for auto-fill. In regards to the passwords that’s probably a bit safer than keeping all the data and the passwords unencrypted in memory. But the cost is that all the other data is stored unencrypted.
I think Stash should cover most of your points, except for the page-less scroll: https://github.com/stashapp/stash The only other software I know for this is Porn Vault: https://gitlab.com/porn-vault/porn-vault
If you want to delete something that is part of your Google account, then yes. Like your Gmail address. But not if you want to delete your account in an entirely different service, that only uses Google for the login. I guess the problem is, that Threads is perceived (and maybe also marketed) as an independent service while it’s apparently just part of your Instagram account.
I use Fedilab for the Twitter-like part of the Fediverse and it has a nice feature, where you long-press the button for reply, star or boost and then you can choose as which account you want to do it.