When I right-click there's under 'Actions' is the 'Open terminal here' option.
I want to move 'Open terminal here' to outside the 'Actions' so it is on the main level when right-clicking.

How can I change the right-click menu and the 'Action' sub-menu?

Hello from the future. Did you ever get this sorted?

Not sure what distro you're using but on mine, the "open terminal here" is in the main right-click menu. Anywho, you could make a service menu which uses xdotool.That needs to be placed in ~/.local/share/kservices5/ServiceMenus
Something like:
[Desktop Entry]
Type=Service
Icon=terminal ( choose what you like)
X-KDE-ServiceTypes=KonqPopupMenu/Plugin
MimeType=all/all;
Actions=Open terminal ( name as you like)
X-KDE-Priority=TopLevel
#X-KDE-Submenu=
Encoding=UTF-8

[Desktop Action Open terminal] (name as the upper action name)
Name=Open terminal (name as you like)
Icon=terminal
Exec=xdotool key alt+shift+F4

The key line here is X_KDE_priority as toplevel which means it's in the main right click. The same principal goes for just about a whole bunch of stuff you'd like to have in the main right click. https://imgur.com/a/Xup2QYr

Same goes for some submenu thingie: https://imgur.com/a/gqhvDho

Btw, here's the desktop file for that menu. Once you know how the principle works, you can do whatever you like. To emulate keyboard shortcuts, you need xdotool of course. As for the rest, scripts, custom desktop files etc...same modus.

[Desktop Entry]
Type=Service
ServiceTypes=KonqPopupMenu/Plugin
MimeType=all/all;
Actions=Embedded;Floating
X-KDE-Submenu=Termcrap
Icon=utilities-terminal
X-KDE-Priority=TopLevel

[Desktop Action Embedded]
Name=Open/Close embedded
Icon=utilities-terminal
Exec=xdotool key F4

[Desktop Action Floating]
Name=Open floating
Icon=utilities-terminal
Exec=xdotool key alt+shift+F4