unlikely

IFF there is a NSA backdoor it likely would be:

- not in paint, but something you can't disable/remove in hardened special purpose windows setups

- not be easily usable by 3rd parties, like some auth accidentally accepting some quite specific other password (e.g. due to some bug reading the expected hash from the wrong place) or similar

lets not forget as much as the NSA might want to spy on you they also want to keep China/Russia out of spying on US companies. A traditional RCE in paint is very counter productive for that.

I believe they're already quite happy with the Windows OS itself for this purpose, and probably some other firmware-level rootkits across many products like Intel and Qualcomm chipsets. Their contracts with Meta might be helpful too.

Et tu, Paint?