can not fill in downloaded forms with latest Mac Pro ios update

Sierra is quite old by Apple's standards!

Released... September 20, 2016 & most recent version September 26, 2019.

But you lis MacOS12.6 which would be Monterey.

Try Acrobat Reader DC...

Adobe Acrobat Reader DC Download | Free PDF viewer for Windows, Mac OS, Android

Whew, the world is changing. :(

To find out if it's system wide or user specific, try this...

Open System Preferences>Users & Groups, unlock the lock, click on the little plus icon, make a new admin account, log out & into the new account.

Does it work in the new account?

If it still doesn't work I'd reinstall the OS.

The link I gave is to the free version...

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