Are there RPC calls for correct RBF calculations in Bitcoin Core? Imagine I have a "stuck" transaction using Bitcoin Core (with correct BIP125 signalling), and I want to "unstuck" it using RBF.

Is there some RPC call for the correct fee calculation?

Meaning, is there a call that would help me with creating a transaction that will be accepted in a certain block target, given the current fee estimations? Ideally in the same way the GUI version already does it.

I know it is possible to calculate that using getmempoolentry (ancestorfees and ancestorsize) and estimatesmartfee, but that is non-trivial.
If your transaction is from Bitcoin Core's wallet, you can use the bumpfee command. It should do the same thing that the GUI does in order to create a replacement transaction with a higher fee.