MacBook pro connects to mobile hotspot but no internet

Blackcap33 Said:

“...there is no data passing between phone and MacBook. I have no idea what's changed and I need the data connection for work fairly urgently.”

Reset your SMC and Your NVRAM.

• How to reset the System Management Controller (SMC) on your Mac Apple Support
• Reset NVRAM or PRAM on your Mac - Apple Support

Changes Occur, and sometimes your Mac needs to reset itself and get back to its default operations.

If connections of sorts are not working, then what seems to be the issue is that caches are getting in the way of interoperability.

With too many temporary files, this must be cleaned. So perform the above.

blackcap33 Said:

"Same behavior again."

AASP (Apple Authorized Service Provider):

With Samsung being an involved device, other than Apple Support Communities, I recommend taking this to an AASP (Apple Authorized Service Provider) --- One, who can offer you the service of Data Recovery.

Go Here: Find Locations - Apple Authorized Reseller. Click: Service & Support > Enter your location information, and see if there is an AASP nearby. Contact one that pops up, and find out more about the data recovery services that they offer to fix this.

Are these both accessible to iCloud?

If so, just upload them from the the Samsung S9 and download them to the Mac (and vice' versa').

I would also try removing the connections, and then adding them back in.