I remember Romelu Lukaku being a great striker too until he moved to Chelsea.... After that his performance got worse... Even now that he's playing at Inter, he can't get back to his best past results... It could also happen to Kane if he changes teams and leagues... I guess it's all about habit and age... If you're not young, it's harder for you to change your familiar surroundings...
It is difficult to compare the two players, Lukaku has experienced a decline in performance because an injury has disrupted his career and after that it seems difficult for him to get up so he becomes an unstable striker, while Harry Kane can be said to be stable and can be said to be far from injury, in every season he plays quite a lot for his club and his contribution is also big enough, that the two players really can't be compared.
Harry Kane will probably adapt to his new club if he really goes to the Bundesliga because if he fails to do so he will become a player with a high transfer fee because that is what his current club wants with a failed status because his arrival does not have a positive impact, if that happens will affect his career in the England national team, so I think he will try to find a way to adapt if he does move, but the question is whether he wants the move?