Child Theme PHP files not working, child css works fine

Hi Scott and Everyone.
I hope someone can help with this , I’ve been tearing my hair out for a couple of days now!
I am having a problem with my decode child theme.
It is set up in the usual way with a child theme folder and a new CSS with the normal stuff at the top fo the CSS:

/*
 Theme Name:     decode Child Theme
 Description:    Decode Child Theme
 Template:       decode
 Version:        1.0.0
*/

@import url("../decode/css/style.css");

/* =Theme customization starts here
------------------------------------------------------- */

The Child theme is active.
The style.css in the child theme seems to work fine.

The problem is that when I edit php files (eg page.php) nothing happens, yet if I make the same changes to the original files in the Parent Decode theme, the changes work.

The php files are in the root of the child theme.

I am developing the site locally using aamps.

Do you have any idea whhy this could happen? Do you need any more information to help?

I have been having other problems which I posted questions about,

But I realise now, they all come down to this.

Thanks