Canon EOS R5C Manual page 724

Registering Menu Items on My Menu Tabs
1.
Select [MY MENU*: Configure].
2.
Select [Select items to register].
3.
Register the desired items.
Select an item, then press <
Select [OK] on the confirmation screen.
You can register up to six items.
To return to the screen in step 2, press the <
>.
724
> button.