It’s a good move on a yearly basis to remove the rear wheels for a clean.
If you undo the centre bolt, the main wheel comes off to reveal a small cog that drives a big cog fixed to the wheel itself. Lift the deck up a little, support it on a block of wood, brick or whatever.
These gear wheels pick up dirt and this needs to be scraped away.
You’ll also see a spindle that the wheel spins on, and some grease here helps.
Give us a pic with the wheel off and I’ll take it further as the drive gear is next!
John
(Wearing a hooded anorak)