Great idea to add a LCD display! I'm not much of a programmer so I'd have to dive in and try this but my time does no allow for that...

Did you try to update the display before/after the button action?

As you have seen, there is a keyboard.begin and keyboard.release. DO NOT put any other code in between those. So I would expect not any problem if you perform other actions before keyboard.begin or after keyboard.release?!

void press_F2()
{
Keyboard.begin();
Keyboard.press(KEY_F2);
delay(100);
Keyboard.releaseAll();

Other than that I cannot come up with any suggestions...
I think other more experienced programmers on the Arduino forum CAN help you out...

I do hope you'll succeed, don't give up on this! ;) I spent 95% of my time getting rid of errors but at the end it did work...

Erik

Sir, what an amazing version of my DCF clock you made... I'm very, very impressed... I can't surpass your designs in a million years. I always admired your clock building skills... Thank you for mentioning my DCF clock from which you made this beautiful improved version. Greetings! Erik

Hello Peter, sorry I only today saw your question...
I can't make modifications to the sketch as you asked because I have limited ability to use a PC due to my health.

Beside that, I think most controllers have an encoder connection option... If not, I don't know how you would be able to get a encoder to work??

So it's a limitation of your controller I think. Maybe you can someday upgrade your controller... Eding CNC has very good controllers for not too much money.

Enjoy your CNC hobby!