My php code is keep getting disable in wordpress editor after upgraded into latest version

My website had a older version of wordpress. Recently I upgraded it to the latest version. After that my php code what I write in the editor is keep getting disabled.

The old page which has php code in ti still works. Although in the editor the php codes are disabled. But if I try to save that it stops working. So i cannot update those page. And also I cannot create new page with php code in it

Exec-PHP plugin is installed.

If I write

<?php echo $c; ?>

It converts into

<!--?php echo $c; ?-->

How to fix that

attached image for better understanding.

Answer

Thank you all for responding.

Apparently I find the solution by installing the Classic Editor plugin

https://en-gb.wordpress.org/plugins/classic-editor/

It prevents disabling the php code.

If you are facing similar problem you can try this one