I'll offer a suggestion.
It may work for you.
Or... it may not.
But...
the only way you'll know is if you try it.
There is an old, but still usable (at least up to and including Mojave, which I still use) preference pane called "rcdefaultapp" which is superior to anything else out there.
It's now discontinued by its author but it's still available here:
Download RCDefaultApp for Mac - System Preferences pane that offers you control over which applications should be used by default when dealing with certain file types
mac.softpedia.com
I suggest you download it and put it into:
(root level) System --> Library --> Extensions.
Then, reboot.
Open system preferences (or settings).
Is the Default Apps extension "there"?
If it isn't, I'm guessing it doesn't work any more.
Just trash it.
If it IS THERE, then I'm going to guess it still works (at least for now).
So, do this next:
Click on the "extensions" pane.
Scroll down (a long way) until you see "text".
Click it and look to the right.
It will show you the default application for "text" files.
You can click on the popup -- do so.
You mentioned the app "Sublime Text" -- is it there?
If so, select it.
If it's NOT there, try the "other" option at the bottom of the popup menu.
It should open a dialog that lets you select any app in your applications folder.
Select Sublime Text and see if that "takes".
Now, close System preferences and try double-clicking on the file in question.
Did this work for you?
Again, you're not going to KNOW, unless you TRY it.
EDIT:
I just tried it for myself.
I downloaded Sublime Text.
Open RCDefault app and set it to be the app to use for file extension "text".
Double-clicked on a text file on my desktop.
It opened into Sublime Text.
So... it seems to work here, using Mojave.