Hi!
Yup, a known issue unfortunately. Your “R” button is most likely ripped off from the motherboard inside the joy-con. The only way to fix this is to repair the traces and solder the switch back on it (if this one is still OK, otherwise you need a new switch).
This do require soldering and some serious soldering skills…
Tho, There is another option and that is replacing the motherboard. There are plenty of them available at AliExpress, way easier, but more expensive.
If you need guides or links where you can buy the Switch/motherboard, please let me know!