As title i got me an old steel road bike i use on the turbo trainer. Did a bit of measuring and it turns out the seat is to low.
Tried to adjust but seized solid. I’ve tried wd40, freeze and release, penertrating oil but nothing is working. My last resort is a blow torch, just fishing for suggestions before I use heat and wreck the paint.

Cant you take seat off and just heat the post and not the frame,? Heat will transfer down
That way the frame will be ok but post may be borked

Filling the frame with Coke worked for me. Left it to soak overnight. Came free easy in the morning.

For me, penetrating oil (left overnight) then more oil and a hair dryer on the frame did the trick. Good luck.