Here's my permissions file:
https://pastebin.com/uur5m8tb

Basics permissions work fine but - -modifyworld.* doesn't work. Default users still can destroy/place blocks etc.

I am pretty sure that was disabled in a previous version.
Anyway You might be able to find a plugin that does what you want for your?
If you can't it wont be too hard to make. Contact me I will make it for your for free.

@Wherkamp please stop.

Anyway you need a plugin called ModifyWorld. It was in pex but was removed into there own plugin.

Unfortunately PermissionsEx is currently unmaintained and no further updates are planned. Because of this, all issues are being closed. If you are looking for an actively maintained permissions plugin, take a look at LuckPerms. It is compatible with major server platforms and can import data from PEX.