Since yesterday afternoon whenever I try to edit any games in the browser, it is simply stuck on "Loading...", so I can no longer continue progress on the game.

Any ideas what might be causing this?

More importantly, is there a way to access the raw text so that I can at least save my progress if I move to another platform?

You can view your code with any text processor. It is just text.
Is there is long list of messages in the box? or where does it stop?
If it stops before it gets to:

Finished loading files
Initialising elements...
Loading editors...
(There is a short pause here before it jumps to your game.)

Then, I think, your Quest program lost a few files, or got corrupted...
You may need to reload Quest.

This is in the browser.

The list of pages populates on the left box, but central box in the editor only shows "loading...', nothing can be accessed.

This isn't specific to the game, it's all games, in different browsers, and different devices.

Yeah, I'm having the same problem, and my game goes live to my fans
on the 15th.

On line???
There has been server problems in the past...
this could be another one of them.
That's why I always download games and play them on my PC, no problems that way.