OP links the Banana Pi M5, VIM1s, Odroid C4, Rock 3A, and the Orange Pi 5 4GB as potential alternatives, but the hardware is not the problem, it's the software support and the community. I'm curious if you've found any SBCs out there that might be viable alternatives to the Raspberry Pi ecosystem.
I've been thinking about wetting my feet with homelabbing a k8s cluster with used OptiPlex workstations. I wonder if Pi's will actually come back in stock or if some other SBC will eventually rise up and start eating away at the Pi's market share.
If you're after "I can run a small k8s cluster on it as part of a home lab", there are various x86 setups that you can build off of.
If you're after "I want a small device to tinker with" then things like https://onion.io ( https://community.onion.io ) may be a direction to look (and it isn't new - its been around for the better part of a decade https://news.ycombinator.com/item?id=12127161 )
https://www.amazon.com/s?k=stick+pc&s=price-asc-rank
edit: tindie dot com and crowdsupply dot com are fun to browse around on