I'm the kind of person who reinstalls linux to change distro and copies over my installation folder for my browser. A long time ago (back when it released in 2014/5) I would do this with windows too. Usually I would get to keep my browser perfectly intact, tabs and all.

That's harder on Linux, with Windows I usually had to only copy appdata for the user and everything would be flawless. I don't know exactly what's different with Linux Vivaldi installs, but it almost always breaks like this.

There are Singleton lock files in .config/vivaldi[-snapshot] that can be deleted if the profiles aren't protected by a keyring.

If the profiles are protected by either KWallet or Gnome-libsecret, you need to unlock that keyring before starting Vivaldi. If you moved to a KDE or Gnome desktop environment from something like Niri or Hyprland, or vice versa, this can happen.

With Vivaldi closed, back up ~/.config/vivaldi/ or ~/.config/vivaldi-snapshot, then try launching with the original backend:

vivaldi-stable --password-store=kwallet6

vivaldi-stable --password-store=kwallet5

vivaldi-stable --password-store=gnome-libsecret

vivaldi-stable --password-store=basic (only if the original profile used it; not recommended for regular use) I had to do this when I went from Hyprland to KDE Plasma and KDE Wallet made it so I couldn't open Vivaldi when I logged into the Hyprland session.

For KWallet/libsecret, the original wallet must also be available and unlocked.