Late 2027 or 2028 most likely. MacOS version lifespan is about 3 years give or take so we'll have a better idea once they announce whether or not MacOS 16 (Sequoia's successor) will support Intel Macs.

I have a hunch we'll get one more MacOS version with Intel support since they were still making Mac Minis and Pros with Intel chips in the first half of 2023.