Keep your work projects in one folder and let git switch identities by path. In ~/.gitconfig:
[user]
name = Imre Csige
email = [email protected]
[includeIf "gitdir:~/work/"]
path = ~/.gitconfig-work
And in ~/.gitconfig-work:
[user]
email = [email protected]
signingkey = ~/.ssh/id_ed25519_work.pub
Every repository under ~/work/ picks up the work settings. Check which one is active with git config user.email inside a repo. The trailing slash in gitdir:~/work/ matters.