This is fixed in Textastic 10.8.6 which was released today.

Can you please try if a restart of your device fixes that issue?

On my iPhone running iOS 26.1, that triple finger menu is displayed differently, not as in your screenshot. 

Here is a screenshot:

Good news! With the help of another developer, I found a way to tell the system that it should open files in the same window instead of creating a new one.

So this will be fixed in the next update.

I've debugged this issue on iPadOS 26.1: the system creates a new window (UIWindowScene) before telling Textastic to open the file.

I've tried various ways to prevent creation of a new window, but unfortunately I found no workaround.

So, this looks like a new system behavior on iPadOS 26.1 that cannot be changed by Textastic.

I also see the same issue when opening a file with other apps like iA Writer, Taio or Runestone.

Hopefully Apple changes this in a future update.

I can reproduce the issue on my iPad. I'll try to find out what's going on. This definitely behaved differently in earlier iPadOS versions.

As a workaround, please use the "Open…" command in Textastic to open files from the Files app in the current window. Or use "Add External Folder…" to add a folder from the Files app to Textastic's sidebar (if supported by the file provider).

Sounds like a bug - I'll investigate. Only the #Textastic folder in Local Files is used.

Thanks for letting me know!

The update is now released on the App Store.