I have a 1080p monitor connected to my PC to the only HDMI port on my GPU and I want to be able to see 16:10 resolutions in my games in addition to 16:9. This is so I can set a 16:10 resolution in my game while streaming to the Steam Deck using Moonlight. This would get rid of the black bars on top and bottom on my SD while streaming. I've read that custom resolutions might be an option, but Nvidia doesn't allow them with DSR enabled which I use as well.

I think all I need is Windows to 'see' additional resolutions while my 1080p screen is off. Would something like this offer these additional resolutions?

https://www.amazon.co.uk/gp/product/B07YMTMMH5/ref=ox_sc_act_title_1?smid=A3VNGL58NT1OOB&psc=1

The dongle would be connected to the GPU and then my 1080p screen connects to the dongle. I wonder if this would let me choose a 16:10 resolutions in addition to 1080p.