Link commits from submodule to the parent repository

Hello!
I have the following situation:

– parent repo (here I write my issues)
— submodule repo1
---- server app
— submodule repo2
---- client app

My question is can I link commits from sub1 and sub2 to issues created in parent repo?

Yes, just use the <user>/<repository>#<issuenumber> notation, which works across any GitHub repository. Issues thus mentioned in commits messages will show a link to the mentioning commit in their thread.

See:

https://docs.github.com/en/github/writing-on-github/working-with-advanced-formatting/autolinked-references-and-urls