That's to be expected, at least I've met the same thing myself
You could play without the UI folder, but if you really want to, I'll explain quickly what to do but it can be a little technical and this is something you'll need to re-do when the game will be updated since they still release new DLCs
You'll need Switch Toolbox and Nxdumptool
https://github.com/DarkMatterCore/nxdumptool/releases https://github.com/KillzXGaming/Switch-Toolbox/releases/tag/EXPERIMENTAL_LATEST
With nxdumptool you'll have to extract the menu.sarc and common.sarc files. Don't make the same mistake than me, with nxdumptool you can choose if you want to explore the base game, updates or dlc. Explore the update, not the base game (the base game menu and common.sarc does not contain Link BoTW for example, it's not too much trouble to deal with but you can save yourself the steps of having to add yourself entries)
You can use this video, it'll explain better what to search and how to replace icons and stuff. I've time-stamped the moment where he talks about modding the UI as I don't think he's talks about nxdumptool.
When you are done, you can save with switch toolbox and you'll have 2 new menu.sarc and common.sarc files, that you'll put into contents\0100152000022000\romfs\UI\cmn and the game should launch properly with the icons and other UI stuff you've modified
I hope it was helpful
EDIT : When I talked about nxdumptool, I was talking about steps you could do if you were on a real Switch. Are you trying to mod the game with Skyline ? Because in that case I don't know how to extract the files from the game, you'll have to search that yourself, but if you can do that then the next steps should be pretty much the same