I believe you want to change the port you want to forward to the Destination Port, not Source Port. The below configuration was working for me previously, but I no longer use port forwards.
Yes the source port is why. Note the (!) there by Source Port, that warning is present because it’s being used in a way that’s almost certainly incorrect (but can be correct in some rare edge cases, so we don’t prohibit it, just warn). If you hover over that warning, it explains why it’s there. Just says that source port is almost always random and should be left to Any.