Can I pair an iPhone 12 mini with a series 1 Apple Watch?

It's technically possible to pair a watch 1 or 2 to a newer phone,but in reality this is proving almost impossible for just about all the 1&2 owners on this forum.

Newer phone's require the watch to have updated hardware to cope with ios 14 or 15 and unfortunately because of the age of these watches the hardware is very limited to what it can do.

Then there is the subject of storage,these watches have very little storage space and the average software update now requires gigabytes of space rather than megabytes and again these watches are very limited with the amount of storage space they have.

It is recommended that even a watch 3 should be unpaired and repaired in order to free up enough space to update.

Yes, you should be able to.