How to prevent PA system from interference of 4G signal
I've worked on small PA systems for weekly gatherings for about 20 years.  The problem you describe is common, but usually fixable, and usually indicates a design issue with the wiring of the PA system.  I've never had any success with filtering, every success was from changing the wiring.

Describe the wiring totally; the type of connectors, the number of wires in cables (balanced, or unbalanced), where the cables come from and go to, and the type of amplifier.  Photographs of the amplifier would help.

You may be able to shorten this effort by testing one channel of the system at a time, with other channels disconnected.

If a particular channel is sensitive to the problem, change to balanced cabling and test again.

Check the earth of the system exists in only one place.

If the wireless receiver unit is separate from the PA, disconnect it and use another device to listen for the noise.  If you truly have noise arriving with the wireless signal, you'll probably have to replace the wireless receiver.