I was confused about this for a while too, but it should work fine.
The UI has a DPI scaling system going on. There’s some option to tweak it in project settings but the default setting is probably fine.
If you try scaling your UI in the UMG editor (if it’s not custom size) you’ll see it starts telling you different DPI’s in the lower left corner. The UI should pretty much display correctly on different resolutions. The only thing to worry about is different aspect ratios, but I basically make sure I handle that with good canvas anchors, or scale boxes.