Hey hey - in QFG4, forgot to pick up the Dark One Sign at the cave entrance. Is there a way back to it as a Wizard, or is this a restart situation? Levitate didn't help, I'm afraid.

It's been a while since I played. I know it's possible to back. The Thief can use acrobatics on the ledges. The Fighter can push the Squid of Stone to tip it over and climb it. With the Wizard, you can do the same with force bolt. It might take many tries if your force bolt isn't powerful enough. If it's too weak, increase its level by practicing.

You can also use "Trigger" to make the Squid Stone fall over

Regarding Wizards, for me, only Trigger works.

I can't even try Force Bolt as nothing happens when I try, nothing shoots, there's no message, nothing. It just removes mana points...
If I try Frost Bite, it states "That didn't do anything useful". Here too it just removes mana points...
Flame Dart and Lightning Ball at least shoot at the Squid Stone, but don't make it move. This is with full stats and the latest version of the game and ScummVM.

The methods that have proven as working are detailed at https://questforglory.fandom.com/wiki/Squid_Stone.

If you try to Levitate as close to the ledge as you can, and go all the way up to the top of the screen, the game should play a message that clues you in on the Squid Stone.