Also, what user is your script running as? On an Apache server it’s typically www-data. Make sure that user has permission to write, move, and delete files.
running 2.4.1, apache, not sure how to tell you “what user” and or if the user is www-data as well as permission.
If you temporarily add this to the your config file, it will tell you what apache user the website is running as. <?php echo exec('whoami'); die; ?>
Then, you will need to make sure that user has ownership over all Kirby files using chown -R /path/to/kirby on the command line.
And maybe this can help with appropriate folder permissions: "This page is not writable"
using chown on my current user did the trick.