Uninstall problems

I've made a copy of this site and it's running locally on our network so I could test the removal of these items before doing the work on our live server and I've been trying to uninstall the following products before migrating to Joomla 4:

Regular Labs - Better Preview
Regular Labs - Modal
Regular Labs - Extension Manager

I first tried to uninstall both Modals & Better Preview using your Extension Manager component by clicking the red "x" on the corresponding items but it just kept spooling and nothing happened.

I then went to Extensions/Manage/Manage to uninstall these products and I ran into errors like this: Joomla\Filesystem\File::delete: Failed deleting inaccessible file with a different file name after each error.

These are the specific 8 items I'm trying to remove now:

Action Log - Regular Labs - Extension Manager - Plugin
Button - Regular Labs - Better Preview - Plugin
Button - Regular Labs - Modals - Plugin
Regular Labs - Extension Manager - Component
Regular Labs Library - Library
System - Regular Labs - Better Preview - Plugin
System - Regular Labs - Modals - Plugin
System - Regular Labs Library - Plugin

I was hoping you can tell me which folders I can delete manually via ftp that will remove all of these items? That would be a great help. Any assistance you can offer would be appreciated. Thanks in advance!

I did check Extensions > Discovery and none of these were there. I'll try reinstalling and uninstalling and see what happens.

With Modals, I had the Pro version, which I stopped using and subscribing to sometime ago, so I cannot reinstall the normal version of Modals to replace this. This is the message I receive:

Error
You currently have the PRO version installed.
By upgrading to the latest FREE version, you will lose functionality.
If you want to keep all functionality you will have to buy a PRO version.

To be able to upgrade to the new FREE version, you will have to uninstall Modals first.

With Better Preview, I reinstalled it without issue but hen I go to uninstall System - Regular Labs - Better Preview plugin, I get the following message:

An error has occurred.
0 Joomla\Filesystem\File::delete: Failed deleting inaccessible file ar-AA.plg_system_betterpreview.ini

Please advise...