When I access Google Cloud, I see some projects that I haven't created. It seems I can't delete them too, I lack permissions to manage them. I am not using anything from Google Cloud at the moment and want to get rid of all of them. Also one of these projects are listed on Firebase as well, where I also don't have permission to delete it.
I haven't seen any evidence that my Google account has been compromised, Gmail activity seems to be fine, haven't seen any suspicious access in Gmail, and I have 2FA activated. The security checkup page in myaccount.google.com shows all green as well… So I'm really confused on how someone could access my Google Cloud account and create projects that I don't have admin access in.
So the question is, how can I delete these projects from my Google Cloud and Firebase accounts?
TL;DR: these projects probably weren't created by my user, even though they show on Google Cloud and Firebase console, so most likely my Google account wasn't compromised. It seems it's possible to include users in projects without them having any say in it, and then these projects show in the console and there's no easy way to have them removed. Apparently they showed up because of my account's Google Groups subscriptions. I removed myself from all groups and the projects disappeared. I wasn't the only one with problems removing myself from projects, as we can see on this issue and this issue, opened in Google's issue tracker.
Additional information: I just got an answer from Firebase support (I had opened an issue with them regarding this problem). They explained that project owners are allowed to add Google Groups to their projects, and anyone who is in that group will have that project show up on console. The easiest way to get rid of that project is to leave the group.
Best Answer
NOTE: This answer is anecdotal, but still probably relevant.
I encountered a similar issue a little over a year ago. It turns out there's a bug somewhere in Google's systems: if you are a member of any Google Groups, other members' projects show up in your project listings. Since you don't actually get any access permissions to those projects, Google did not consider it a security issue when I reported it and decided no action was necessary.
You can check which groups you're subscribed to here: https://groups.google.com/my-groups; and leaving them should automatically remove the projects from your project listings.
Originally posted as a comment.