Why don’t you try it yourself and find out? It’s easy to do.
Its very hard for anyone here to conclusively answer this for what you’re asking.
I wonder what it is that even a VPN obfuscation is not enough for you. It can’t be illegal cause Twitter would take it down so why is a VPN not good enough?
Is not always the case. Try to use additional obfuscation methods Mullvad provides so the platform doesn’t flag your account or shadowban you. It may not may not work still but no harm in trying.
I’ve never done it. But I guess if you had to, you’d probably have to use an offline/local password manager, like KeepassXC, to save the password for your twitter account.