I used this registry update to set vscode as my default text file editor (copy & paste into update.reg, open regedit and import the file):
Windows Registry Editor Version 5.00
[HKEY_CLASSES_ROOT\SystemFileAssociations\text\shell\edit\command]
@=hex(2):22,00,25,00,55,00,53,00,45,00,52,00,50,00,52,00,4f,00,46,00,49,00,4c,\
00,45,00,25,00,5c,00,41,00,70,00,70,00,44,00,61,00,74,00,61,00,5c,00,4c,00,\
6f,00,63,00,61,00,6c,00,5c,00,50,00,72,00,6f,00,67,00,72,00,61,00,6d,00,73,\
00,5c,00,4d,00,69,00,63,00,72,00,6f,00,73,00,6f,00,66,00,74,00,20,00,56,00,\
53,00,20,00,43,00,6f,00,64,00,65,00,5c,00,43,00,6f,00,64,00,65,00,2e,00,65,\
00,78,00,65,00,22,00,20,00,25,00,31,00,00,00
After that the registry is updated as follows:

Of course you should not trust hex encoded registry updates you found in the internet. So copy 22,00 ... 00,00, remove all backslashes, linebreaks and whitespaces and convert through one of many hex to ascii online converters to verify the import:

After you made this change you can even edit text files with vscode through the "edit" context menu entry:
