That comes with a big caveat. You can either choose to use the printer offline, or online, with no ability to use both. If you want the ability to monitor or pause a print when you're not home on the off chance something goes wrong, you HAVE to send every print through their cloud, there's no middle ground.
That's not Bambu being open, that's them doing the absolute minimum to allow people to say "you can use Bambu printers fully offline" in comment sections.
Wait, that’s still just about their phone app. When you disable the cloud features, you lose the phone app, but otherwise the printer is fully usable. You can still connect to it through Bambu studio, you just have to roll your own networking (e.g. a VPN), right?
Can you access all that on you local lan though?
If so then you could access it over a reverse proxy like Tailscale.
Its trivially easy to set one up these days.
Monitoring is still possible with Tailscale and Bambu Companion (or a number of third party apps you can put on a Raspberry Pi or similar)
https://testflight.apple.com/join/VXBxZYNr
https://bambuddy.cool/