Yes, very definitely. The new 4 GHz 5G transmitters are now adjacent to the existing downlink band and are causing interference to those users as well. Your dad might have to get an LNB with specific filtering or a separate filter and that might not work if the transmitter is close enough. Hobby dish owners have no protection here. They can't exclude 5G transmitters from their vicinity like a commercial dish operator.
Relevant discussion:
* https://www.intelsat.com/wp-content/uploads/2021/02/intelsat...