I was playing the human campaign on Tides of Darkness when I beat the second mission in the campaign, I hit the save button when I got the victory and when it started to show how you did in the mission it the game crash. I couldn't do anything so I had to turn my computer off. (I am also not playing on the classic version).

Is this a know issue? If I dont save when I get victory prevent the crash?

Im personally get used to make saves just befores level/mission exit. In shooters and strategies. Many have no restart function and use start_autosave or your manual save to restart which is sometimes make minor issues.

Technically there is no issues preventing game to be saved at any time nor CTD at the end of missions. Try validate the game files in Galaxy for Galaxy build version. Or reinstall if it is offline GOG version.
Look to PCGamingWiki and its Config/saves location article sections. erase config bafkup save (optional).

Maybe there is more useful info for you there. Or on GOG Support link there.