They completely ruined his character in Last Jedi, and now we are finally seeing him do something a lot of fans wanted to see from the beginning. TRAINING HIS STUDENTS. Not him being a miserable failure like they presented him in the ST.
I find Luke to be more out of character in TBOBF then he is in TLJ. As we see in that film, Luke nearly turned on Ben because of his attachment to Leia, Han etc (“everyone I loved”) and has yet another impulsive reaction to those loved ones being threatened, as he does in the original trilogy. In TBOBF, the man who has loved his friends for years and whose own father only turned back to the light side because of his attachment is strictly preaching the ‘no attachments’ rule and denying Grogu the relationship with his father figure.
Either that is setting up him trying to follow the ancient Jedi dogma too strictly and failing as he indicates in TLJ, or it is out of character.