The Brief: "Purr" is used to signal finality, as well as, excitement and/or approval.

DEEP DIVE
Purr is a slang term used to indicate excitement and/or approval. It also signifies finality. According to a June 13 definition on Urban Dictionary, “purr” is used similarly to “period” as referenced by Rolling Ray.
brittany: i broke every bone in my body
us: purr ๐ป๐ป— tired๐ป| she/her (@lovvemygrande2) July 29, 2020
Blue is giving the girls a natural look with a red lip, purr ๐ pic.twitter.com/3jYYLAEShI
— ๐ฐ๐ก๐๐ซ๐๐ฌ ๐ญ๐ก๐ ๐๐ฅ๐๐ฎ๐ฆ ๐๐๐ฅ๐๐ง๐๐ซ๐ข๐? (@GlowKellys) July 30, 2020
Just got a snowcone purr pic.twitter.com/USvP5D7XIZ
— HOOD VOGUE is tired of poverty (@itskeyon) July 29, 2020