We will add more correct layout for single.php file. But looks like their default design theme has bug and doesn't work with correct files. However, they wrote you correct answer. Swift design theme is working without bugs
Before all pages is like attachment, now just article, i ask help to AMP for WP team aslo,
I think it's them who change template and find solution for page and categories:
I need admin access
When i use your template with AMP for WP, i have no AMP header and menu.
If i change template, it's work normally.
I desactivate AMP in theme option but nothing change.
You can see here:
Link on page with issue (Optional): https://meilleur.xyz/amp/