Logout After 10 or 20 Minute Issue

You have to change default session time in php.ini file.
To Open the file.
sudo mousepad /etc/php/7.4/apache2/php.ini
A text editor will open. 
To find variable session.gc_maxlifetime Press Ctrl + F and paste this variable.
It'll find the session.gc_maxlifetime.In front of that the default value is 1440 second that is 24 Minutes.

Change this value to 14400 that is 4 hours.

After changing values Press Ctrl + S It'll save the file. Then exit by Pressing Ctrl + F4.

Hope this will helpful for you.

Thank you.