I can see why that might be a useful feature, but there are pragmatic ways around it.
My view on that is if you don’t want the ROM on the Steam UI, don’t load the ROM onto the device. Or keep Steam UI ROMs and non-UI ROMs in separate folders, and move the ones you want added to the Steam UI to the folder as and when you’re ready to play them.
The way I do it is I store all my ROMs on my home server, sync them to my gaming PC (as I have everything installed on my PC) and then access the network share on my Deck and copy games over when I want to play them. It’s not like I have enough storage on my 512gb SD card to have everything on it all at once.
My view on that is if you don’t want the ROM on the Steam UI, don’t load the ROM onto the device. Or keep Steam UI ROMs and non-UI ROMs in separate folders, and move the ones you want added to the Steam UI to the folder as and when you’re ready to play them.
The way I do it is I store all my ROMs on my home server, sync them to my gaming PC (as I have everything installed on my PC) and then access the network share on my Deck and copy games over when I want to play them. It’s not like I have enough storage on my 512gb SD card to have everything on it all at once.