No, ”git add .” is not easily reverted, there’s no git sub command for de-adding files from the staging area. You have to copy the whole folder (hope you have enough disk space), checking out an older commit (hard), and copy specific files from the copied folder. Pita.

This is actually a general problem with git and most cli tools, where it would be possible and useful to undo an action, but the tool developer cannot be bothered to implement such time-saving feature.