SMPlayer suddenly "an unknown publisher" (Windows 10)

[Lek]

Yesterday, I made SMPlayer my default player for all video files. And it worked fine.

Today, I discover that there was no default player for videos. So, I again made SMPlayer the default player. But when I clicked on a video, nothing happened.

So, I set the smplayer.exe file run as administrator.

Now, when I click on a video, I get a UAC message "Do you want to allow this app from an unknown publisher to make changes to your device?"

I've been using SMPlayer for years with no such issue.

I would appreciate any suggestions on stopping "Do you want to allow this app from an unknown publisher to make changes to your device?" (aside from turning off the User Account Control)?

Thanks.