i used to say "that's okay" or "no worries" or something in response to apologies i wasn't ready to accept, but felt it important to properly acknowledge
but that kind of implicitly accepts the apology or worse, excuses
but you can acknowledge that someone apologized without doing that. you can just say "thank you for the apology"
it doesn't even preclude you accepting it at a later time, and it's been very freeing for me