Where was the rook captured?

It's been a while since I posted a retrograde analysis puzzle but I've finally managed to create one, and this one is quite tough! This was initially going to be an illegal position, but there's an awful lot of cases to work with and I don't think it would be as fun to prove illegal. While there's still some cases here, finding the solution should be somewhat rewarding.

One of the white rooks on the board is missing. Where was it captured?

I've thought about it and the original problem might be too tricky because of all the cases, and I don't think that makes for a fun puzzle. Here's a slightly easier version which reduces the casework. Same question as before: where was the missing white rook captured?

Last moves are something like this:

The bQ and N promoted on g1.

wR was captured on b6.

For difficulty, this took me longer than usual. I feel a bit rusty on solving retros. It's not trivial, but I have solved problems of this difficulty level before.

Well done for solving the puzzle! Finding this solution certainly was not easy, and there was some tricky retro play involved with all the shielding from checks.

The initial idea for the release was obtaining a black queen and another unit to shield on a5. I still had wPc5 so that bQ could potentially get unpinned on c3, but then I realised the option to retract cxb6, which opened up more possibilities. Eventually, I decided to make the original release illegal and use cxb6 in the new solution.

Do you think the problem is better with wPc4 or c5? wPc5 adds the possibility of more tries, but this also makes it more difficult to tackle.

I prefer the problem with Pc5 for the reason you stated - there are tries involving bQc3 unpromoting on a1. They fail mostly due to not having an extra white unit available to uncapture on c3. This was the first idea I considered.