Textastic's file "Local File" and "iCloud" locations are available in the Files app. See https://www.textasticapp.com/v10/manual/managing_files/local_files_icloud.html#local-files for details.

So, if an app can export photos to the Files app, it can export files into "On my iPad/iPhone" -> Textastic or iCloud Drive -> Textastic.

Hello,

yes, but because of the interface and style changes in Big Sur this isn't done with just a recompile. Meanwhile, the current version works very well on Apple Silicon Macs. I'm actually writing this on my M1 13" MacBook Pro.

Can you please tell me what exactly you were trying to do that didn't work.

Do you mean the "email support" button in the app? 

Please use the "Open…" command in Textastic to open files from the Files app using the iOS document picker.

You can also use "Add External Folder…" to add folders from iCloud Drive or apps like the Git client Working Copy as an external folder to Textastic.

Have a look at this topic in the manual for details: https://www.textasticapp.com/v9/manual/integration_other_apps/external_files_folders.html

Looks good. Do you see the "iCloud" option in Textastic below "Local Files"?

I'd try a reboot of the device.

That's not the right setting. Please look in "Apple-ID" -> iCloud. There should be a long list of apps including Textastic. Please check if iCloud is enabled for Textastic there.

Do you have iCloud Drive enabled for Textastic?

There should be an "iCloud" option in Textastic below "Local Files" and there should be a "Textastic" folder in iCloud Drive that has Textastic's app icon as seen in the screenshots at https://www.textasticapp.com/v9/manual/managing_files/local_files_icloud.html#icloud

Textastic's "Local Files" can be found in the Files app in "on my iPhone/Textastic". "iCloud" can be found in the Files app in "iCloud Drive/Textastic.

Also, the latest version of Textastic added a "Get File" shortcuts action that lets you retrieve and file from "Local Files" in Textastic by path.

I'm sorry, but I didn't completely understand the request. What are you trying to achieve, what's the use case?