I have learned that you can set the default boot device in control center.

I recommend post a picture of your control center.

Yes I can select the default Operating System to boot; but how to configure it to be dynamic (always boot from the last manually selected option).
I configured these variables in the /etc/default/grub file and it works. But an option from the Control Center for that would be great
GRUB_DEFAULT=saved
GRUB_SAVEDEFAULT=true

From your feedback I can see that your startup delay function were disabled.Try to enable it.

After that,you can directly boot what system you want to use form the grub,just use"↑"and"↓" of your keyboard,then press Enter.And if,your most commonly used system is Windows, you can choose the default system as Windows after turning on startup delay.

Yes, I know that using the arrow keys I can change the operating system to boot; but making it dynamic to always load the last device booted could be a big improvement for your awesome Linux distribution.

All the best

Err,maybe the package "rEFInd" could help you ?

That's a third part tool and you'd better BUCKUP YOUR SYSTEM BEFORE.(because I didn't try this tool before.)