LAST RESORT: Seized / stuck seat post. AVOID CAUSTIC SODA!
This aluminium seat post in a steel frame is categorically bonded and won't come out. We tried everything including trying to cut and saw it out. Our reciprocating saw still couldn't do it.
YouTubers suggest a last resort of Caustic Soda. That seems to wreck the paint on your bike and is pretty extreme.
I have not seen anyone try to drill the post out so I have tried. Unfortunately I could not measure the seat post as it was already destroyed and the top of the tube opened up, so I took the post outside diameter minus twice the thickness and bought a 26mm cutter and an extension for it. O didn't want to cut the seat post itself.