Do you have "Smart Punctuation" disabled in Textastic's settings?

Are you on iOS 13? I'm asking because there is a bug in iOS 13 so that touch scrolling does not work.

Added MoonScript, HCL, and TOML.

Good idea, I just added it to the manual.

Ah, ok, you need to add Working Copy as a location in the Files app for this to work. Otherwise the file provider isn't active. I haven't tried it without that to be honest.

I just tried it on an iPad Pro running iOS 13 beta 7 and it works for me. Please note that you need to drag a repository from Working Copy (not from the Files app) into the sidebar of Textastic (where the "Local Files" and "iCloud" locations are shown).

The latest TestFlight beta of Textastic also has a new "Add External Folder…" option on iOS 13.

You can add iCloud Drive -> DEV as an external folder. Have a look at the manual at https://www.textasticapp.com/v8/manual/integration_other_apps/external_files_folders.html for details.