How do I associate JPEG files on Windows 10 with IrfanView (or other program)?

I was trying to associate from within IrfanView options, but it didn't help.

When did this with "Run As Administrator", it didn't help either.

The right click menu doesn't contain "Use Always" checkbox any more:

Open Control Panel, type "Default Programs" in the search box, and click on the only search result, also "Default Programs".

Scroll down to "Choose default app by file type", wait for a while until it loads, and scroll down to jpg or jpeg, depending on your file extension. Click on the application currently listed, and it should provide you a list of applications to choose from. Select the application you desire, and you're all set.

Note, that if your machine is not your own (for example, a corporately owned workstation at your employer) this option MAY not be available to you.

You need to run iview.exe as administrator, set your associations, and then you can go to control panel, type associations, and it will then let you select iview as the default photo viewer. This even works with the portable version.