Mac connects to iPhone hotspot but no internet

I got the same issue and solved it differently.

In my MacBook, I had the DNS server setup to point to Google's public DNS IP (8.8.8.8 / 8.8.4.4), I simply deleted those registers and left the default. It worked for me, hope it works for you.

After hours of experimenting, and a long and pointless call to my network operator, I finally managed to fix it... by deleting the phone from the list of known wifi networks on the MacBook, and reconnecting. Same SSID, same password, now working fine.

I recently switched SIM, moving to a new carrier. With the old carrier, the MacBook could use the phone's hotspot with no problem. I don't know what info gets stored for a wifi connection (I'd assumed just SSID and credentials) but presumably there's more to it...