cannot re-pair watch and phone with (already) compitable ios

I have been using my watch for a year already. It suddenly demanded to delete and pair again 'cause of incorrect password (tho I haven't use it for a few days and def didn't try to unlock it "too many times" but nevermind).

So,

1. I unpaired my watch and tried to pair again.
2. Now there is a demand for an update as it is reqired to be updated to the latest version in order to pair.
3. But as soon as I try to update my watch, there is a demand to update my phone first. BUT I DON'T WANNA USE IOS 26. I have ios 18 and I want to leave it at this.

Now I don't understand why it pushes me to update if both devices are COMPITABLE and have compitable ios RIGHT NOW. The have similar ios and were working just fine two days ago. Why I cannot pair two devices with compitable ios? Why do I have to update both to the latest version full of bugs?