You're not doing anything wrong.
You are going to get UAC for this, period. If you want true "one click" it just ain't gonna happen.
It can take anywhere between 15 minutes and half an hour for your average "Quick Scan" to complete, as it's given low priority and anything and everything else you're doing in the foreground will get priority.
The output, if you're doing it in a full screen is "Scan starting. . ." followed by "Scan finished" and the window will not close.
For myself, I created a batch file (QS_Script.bat) and placed it in my C:\TEMP folder. It's a one-liner that contains:
"%ProgramFiles%\Windows Defender\MpCmdRun.exe" -Scan -ScanType 1 > C:\TEMP\QSLog.txt 2>&1
[All of the above is on one line].
I create a desktop shortcut that has C:\TEMP\QS_Script.bat as the target and that runs minimized. You still get the UAC prompt, but the minimized command prompt window closes itself if you don't maximize it, so you can tell the scan is done when it disappears from your taskbar. If you feel the need, you can also check QSLog.txt to see if there were any errors or if anything happened to be found.
By the way, the log file will show as being zero sized until the process finishes if the only content is the start/finished messages, as the start message stays buffered until the final write for the finished message.
I ran lots of experiments last night. I doubt my machine has had that many Quick Scans in rapid succession ever!