Suggestions for a good and clean starter / parent theme

Hello fellow WordPress users, as stated in the post title I'm looking for a good starter / parent theme to work on.
To explain the "starter / parent" part I'd like to give you a little context.
At the moment I'm working as graphic designer for a small company, and our website has been hacked (the agency my boss found to maintain it made an amazing work, as you can see).
I was a web developer for about 8 years before working here and I still keep doing small projects, so I fixed the website, but the problem came from a combination of outdated commercial theme and plugins that can't be updated since the agency modified them DIRECTLY, without any child theme…
I proposed to my boss to rebuild the website from scratch, since I don't want to put my hands on the current shit; I always created highly customised themes, starting from scratch, and that's the way I'd like to work this time too (I find block themes and page builders absolutely abhorrent!).
The problem is, I'm thinking about leaving my current job, so I would like to create a child theme starting from a solid theme, so that maintenance can be easier after I eventually leave.
All that said, that's my question: which parent theme could I use to build a custom yet solid child theme? At the moment I'm thinking about Twenty Twenty One, could it be a viable option?
Thanks in advance for your suggestions!