iMac (Intel) with macOS Tahoe 26.0.1 fails to access internet via iPhone 16 Pro Max's personal hotspot

old imac with os catalina 10.15.7 connects to internet using personal hotspot on iphone 16 pro max ios 26.0.1 but imac (intel) with tahoe 26.0.1 shows hotspot connected icon but no internet connection.

personal hotspot definitely works both on old imac and on the ipad which i am writing this on and us also connected via personal hotspot on the same phone.

TIA

[Re-Titled by Moderator]

Original Title: old imac with os catalina 10.15.7 works with iphone 16 pro max ios 26.0.1 but imac (intel) with tahoe 26.0.1 shows hotspot connected icon but no internet