some builders use various loctite stuff on the spokes. Spoke prep and similar things will help increase friction but allow the nipple to turn once you put enough pressure on it to break the seal. It's sort of like paint.

What you probably need to do is break loose the nipple. I was trying to imagine myself truing a wheel after some time and I realized that I'll regularly unscrew a nipple quite a bit to get it so I can feel how much resistance there is, if there's stuff in the threads, etc. The last wheel I fiddled with was a HED so I didn't build it, and it seemed like they had something on the spoke threads. Anyway I'll unscrew the nipple maybe 1/2-1 turn then retighten it the same amount then do whatever truing.

With new wheels I like to lube the nipple/rim junction, I use spoke prep on the spoke threads. If I have to retrue that wheel I usually put a drop of lube on the rim/nipple junction to let the nipple move more freely.

On wheels I don't know I'll put lube on the nipple/rim junction as a last resort, also on the nipple/spoke if it feels like I broke a loctite seal. I don't want the spokes to squawk at me when I turn them.

Disclaimer: I did build wheels for part of my living for many years, I built hundreds of wheels, I've built a front wheel in 20 minutes or so and raced it no problems, etc etc, but I haven't built wheels regularly for 17 years. Never built a wheel with straight pull spokes, not that many with bladed or aero spokes, blah blah blah.