Pocketbase (https://pocketbase.io/) piqued my interest after seeing it here and on ProductHunt, but I don't think it would be the right call for a client before it hits a stable release.
I also very much enjoyed OctoberCMS (although it has its quirks), but there was a fairly acrimonious split in the community there, and OctoberCMS is no longer open source, and I haven't used the fork (WinterCMS: https://wintercms.com/)
I enjoyed using Apostrophe (https://apostrophecms.com/) for a while, but ultimately I felt like I was doing a lot of stuff in a way that didn't come naturally to me, and although Mongo seems a logical choice when you look at Apostrophe's page model, it worried me a bit that the data would not be easy to move if I ever wanted to.