With stock and custom ROMs.

is it still a thing? ik it's not impossible but i haven't seen one in almost a decade. last time i dual booted was on android 4.4.

I'm willing to bet dual-booting will require an unlocked bootloader. There goes your security if this is true.

You could install GrapheneOS on a Pixel and set up multiple users? Up to 32 if you want. Some can have Google Play Services and some of those can be signed into a Google account while others are just using GP Services without signing in.

Much faster to switch between users than booting a second OS.

Pro:

• do most of what needed two phones on a single phone
• avoids charging, carrying, and maintaining two separate phones
• I'd personally put a lot more here if dual-booting Android and Linux

Con:

• hard to find a phone that supports it
• the need to unlock bootloader could still break integrity checks despite using a stock ROM
• IMEI still shared between ROMs, most of the isolation is already achievable through user profiles
• have to reboot to use anything on the other ROM

I know this doesn't answer the question but, I don't think dual booting is the best way for seperation, bcz rebooting is a mess everytime u want to switch. I recommend dual profile or app cloning...

Better use something like Shelter imo.