Is there a way to change the issue UI as it's possible to change notifications template?
I saw a category called Template components where I can customize templates very similar to issue UI.
No, unfortunatelly, some coding is needed to get an alternative UI, as far as I know.
Yes. However, you need to create your own web page and use YouTrack REST API to get data from YouTrack server.
Here are some links that might help you: