I've just had almost this exact same problem.
I'm playing a "journeyman" save where I move clubs quite frequently. I'd worked my way up from Leyton Orient to FC Porto, and I get to mid May 2024 at the end of a very successful season when the Bayern Munich job becomes available. I now have the managerial reputation to stand a chance, so I apply. I go through the interview and, just like @SazoJohnno, I choose the option to take over at the end of the season as I've still got the Europa League and Portuguese Cup finals still to play with Porto.
I play those games and get the contract offer from Bayern, but instead of starting at the end of the season (...say late June or early July 2024) it starts in mid May 2025. There is no way for me to adjust this. Accepting means the FC Porto board will remove a bunch of my managerial powers such as control of player and staff transfers. Rejecting the contract will probably totally ruin my chances of the job.
It's a disaster.