Sooo this just started...
I Was pulling into my drive way last night and went to hit Rear break and a clanking noise came from around my shifter area....And it only does it when it’s in gear
I am stumped..
Any help would be great

Start by checking the chain adjustment, and look for any seized links.

Next would be confirming the sprocket is tight on the countershaft.

Then look at the rear caliper, rotor, and the "cush drive" for excessive play.

https://faq.ninja250.org/wiki/How_to_shim_the_cush_drive

Also check to make sure you dont have any teeth missing from the front or rear sprockets

Probably chain slap on the swingarm from poorly adjusted or worn out chain.