Default program not listed in windows10 settings [duplicate]

If there was really no checkbox for "Always use this app to open .txt files" on your "Choose another app" menu, you might have luck changing your default app settings - which you can either search for on your Windows 10 or:

• Go to Control Panel

• Click Default Programs
• Click Set your default programs
• Click Choose default apps by file type
• Scroll down to .txt
• Change your application to Visual Studio Code

If that doesn't work, you should also be able to do so from command-line using the ftype and assoc commands:

ftype txtfile="C:\Path\To\Visual Studio Code.exe"
assoc .txt=txtfile

Reference: ftype, assoc