How do I make Sublime Text 3 my default text editor on Windows 10?

It's an issue on Windows OS side. Don't worry, I have a fix for you (the only method that works on the Internet):

• Open start menu --> type in cmd --> right click on it and run as administrator

• Depending on where you have your sublime installed, you will have to edit the path, otherwise, copy + paste this line in order to change the .txt extension:

ftype txtfile="C:\Program Files\Sublime Text 3\sublime_text.exe" "%1"

You can follow the same logic by always starting with "ftype" in front and then then you will need to find out what is the abbreviation of a chosen extension. You can do that by typing in "assoc .css"

For example, .php is PHPfile or .css is CSSfile

Screenshot here with some more examples

First go to the windows settings menu, click on the Apps settings. From there click Default Apps, scroll down until you see "choose default app by file type". Click that option, then scroll to the file extension ".txt", and click the gray plus arrow beside it and select sublime text.

Not my answer, but the best I found, UX-wise: https://superuser.com/a/1354363/1034806

As above, in Windows 10 version 1803, , the control panel shortcut now just brings up Settings.

But the following worked:

Right-click on the file, select "Open With" and click "Choose another app" at the bottom of the right-click menu.

Clicking that gives the dialog box with default app selection that ends with "Look for an app in the Store".

Here's the tricky bit: Click on the white space under the last option. This extends the list!

Scroll to the bottom of this list (assuming your app isn't listed).

Click on the white space, under the last option, again!

You should be taken to the Windows standard File Open dialog, where you can browse to your program of choice. (Worked for me.)