I have quite a few things to say about this, so for the sake of organisation I'll split it into three messages.
Firstly, OP mentioned that the battery has been replaced in their 1st generation Apple Watch and that they work on tech a lot. This implies that they opened up the watch and performed the battery replacement themselves. As
@stiligFox has mentioned, a 1st generation Watch running its final supported OS (watchOS 4.x) should still pair and work with iOS 16, so the fact that OP's doesn't is strange. I suspect there may be a hardware fault with their watch.
Funnily enough, I've experienced a very similar issue before. Earlier this year I bought a bulk lot of old tech and among the products was an Apple Watch Series 2. I tried pairing it to an iPhone on iOS 14 and while the Watch app could detect it and initiate the pairing process, it would always fail with an unspecified error. Upon closer inspection, I discovered that the screen had started to come away and the watch's chassis was no longer properly sealed. After a full teardown, I found dust and corrosion inside the watch.
I think this might also be the case with OP's watch. They opened it up years ago, which compromised the physical integrity of the device. While it didn't cause any immediate effect, over the years the ingress of liquids and other contaminants and their accumulation could have resulted in damage to the logic board, preventing it from functioning properly.
If this is the case, then the watch has indeed suffered a "natural" or hardware death, and not an intentional software bricking attempt.
Or put another way: Your Watch has ended.