Dometic Sealand toilet

There is a screen where the water line attaches to the water valve. The water valve is bolted to the spring and shaft assembly under the pedal. You will need to replace the water valve or pull it out and use compressed air to clean it.

Dometic/SeaLand make many different style of toilets

Macerator Type
Vacuum Flush Type
Gravity Flush
Etc.

Gravity Flush have an inlet screen at water supply valve......
Turn water supply off
Place towel on floor under water line fitting....disconnect it

Water valve assembly is a 'snap in assembly'

Otherwise.......what model do you have????

Has it been like this for a while or all of a sudden? Any other work on the plumbing system recently?

Pretty sure there is no filter or screen.

Check the supply pressure, next is probably valve replacement unless it comes apart to inspect or clean.

Is there a shut off valve going to the toilet
Shut off pump, drain water from lines
Disconnect toilet make sure this valve if not clogged with sediment