The S24U S Pen might fit in the S25U (the dimensions of the S Pen itself seem unchanged), but it won't charge or pair with it since the S25U itself is missing the extra coil needed to do so. It will still work as a pen but none of the Bluetooth actions will work.
I'm guessing you'll be able to pair the standalone S Pen pro (the one they released for the S21U and Z Fold3 onwards) and use that for air actions though but that's not ideal given it doesn't fit inside the phone