@SGpro - unfortunately it appears the NVENC limits are defined by the encoder, not the hardware. Having a 3080 doesn't help in this regard.
I can either picture-by-picture my 5120x1440p into a 21:9 + 11:9 and stream the 21:9 section, or I can scale the 5120x1440 down to 1080p - otherwise I'm forced to use a software encoder.