Or Hackintosh. Hey, GP asked 'what machine'. Didn't require it to be an Apple.

I’ve given this thought for an older MBP of mine that can’t upgrade to latest OS so that it can be used as a CI.

My issue with that is 1. Can I trust the hackintosh to not be compromised and 2. Uploading an IPA via hackintosh feels like bananas.

If you use say Proxmox and create your own macOS image and compile your own Opencore then you should be OK. You can do same on VirtualBox. (On a PC, cause I doubt older MBPs have the necessary stuff like VT-d.)

Of course, once Apple kills off x86-64 macOS it is going to become more complicated.

Hackintosh's are dead as soon as Apple stops supporting Intel chips.

That won't be for a very long time. There's a lot of Mac Pros out there. They're still supporting the 8-year old 2013 Mac Pro, the trashcan one. They sold a lot of the revised Mac Pro to animation studios and such. I wouldn't count on support for those being dropped for at least ten years.

That would be the same for OPs use case. He’s using a M1 MacBook Pro so nothing would change. The M1 devices don’t support more than 16 GB RAM, too.

The recently released M1 MacBook pros go up to 64GB.