You should just be able to go into Focus Status and disable it. That will stop the Mac from being able to trigger Focus no matter what. If you really want to neuter it completely, you can delete any Focus modes you see there too.

As for Do Not Disturb, it is usually mirrored from other devices too, so maybe you turned on DND on your phone or triggered a focus mode from there or something?

If you’re just testing on it you can get away wit pretty much anything as long as it’s Apple Silicon. I would think a used M1 Mini is probably your cheapest bet, and as a bonus you can use it as a media serve for Plex of something when you’re not testing on it.

If it’s got to be a laptop form factor, then yes, an MBA is probably your best bet.

And yet Siri is dumber than a bag of hammers…

And I say that as someone who has been using Macs since the 512k in high school.