I suspect the use case for trimming audio and video files is somewhat niche, but still Auvid Tuner UWP might be a useful tool to keep up your sleeve. Perhaps making ringtones, video lopps/clips, and - yes - editing music track ID3 data (at least, if you pay the IAP). Screenshots and details below.
I'm now sure about 'Beautiful UI' - it's certainly simple. Here's the app in action:
The most useful feature for many will be the ID3 editor for music tracks, though this is behind an IAP. Still, you'll get a feel for the UI generally from what's here by default. Notifications are for the end of trimming, for a long video operation, typically. And always good to see a choice of themes.
Trimming an audio file exactly, to the second, plus (right) selecting a video file for chopping down...
Less precise, but you can still use sliders to get roughly what you want - select quality etc. and then hit 'Trim'. Actually doing the trimming and re-encoding takes a while, as you might expect.
Of course, trimming (usually) home-shot video files can already be done in Windows 10 Photos, so the video side of things is a tiny bit redundant here, but you do have greater control here and don't have to mess around getting Photos to access the video material...
You can grab Auvid Tuner UWP for free in the Store here, for all Windows 10 devices, from phones to hybrids and tablets to desktops. In addition to opening up the ID3 editing, in app purchases also get rid of the banner ad, as you might expect.