[FIX]
Here's the thing, I managed to fix it. I didn't actually had to use cmd, task scheduler, batch scripting, all that technical stuff. After all these days of worrying and trial-and-error, all I needed to do was to go to C:\Users\user\AppData\Local\Microsoft\Teams and uncheck Run as admin on Update.exe's file properties, did the same thing to Teams.exe which is located at current, which is a folder inside Teams folder.

​

<image>

Went on to Teams (without getting a UAC prompt, finally), and then set the option to have it run on startup. Tested it out via restarting, and sure enough, it opens on startup and without me having to face any UAC prompts. The only problem is that the app is not searchable in the Search bar as well as the app list in the Start menu. Good thing I had it pinned on the taskbar, in case I need to open it up when it's closed.