No apps linked with the "Open In" Functionality, therefore can't use it.

Were there any updates on the third-party app that you’re using to open this type of files, right before this issue started?

... Not that I am aware of - I believe 'Text Edit' is bundled as part of MacOS - but now you mention it there was a recent update I am now on Ventura 13.4.1 - just checked - there is another update that moves to 13.5.1 - so am going to update and see if that fixes anything.

Is the file in question locally synced to your desktop app? Does it show a green checkmark, when you open your Finder > Dropbox folder?

It does not - but no other files in drop box have that green check either - despite me being able to see them in the web application.

Nancy Mark Rich 

Many thanks all for your help ... so here is the latest state of play.

As per my last email - I have just updated my MacOS - and it is now running on Ventura - 13.5.1

Under Safari - nothing has changed - same problem

BUT

Under Chrome - I now have the option to use Textmate (which is my default app for .md files AND if the file is .txt it offers me ability to open Textpad - which is my default.txt default app - PLUS in both scenarios it also allows me to jump through to finder and see the file in finder - I have not ever seen that option in the past.

My take is that whatever the gods of Cupertino are up to - they are messing with this functionality (though I doubt intentionally - but heh - you never know - right 👿

Also interesting is that I run Chrome because Safari often has - shall we call them 'nuances' - which also points to Cupertino dependencies.

I am happy running with Chrome to do what I need to do - so thankyou for talking me through.

That said - that tool bar is definitely weird. Friend of mine in Austin for example doesn’t even see the tool bar in his browser!

I am good for now - BUT - if there is anything I can do to in turn help you understand more as to what might be going on - more than happy to help you.

Many thanks again.

/JOHN