SSL not fully covering all pages on domain

It’s the default favicon URL. See network tools in Firefox:
On a page without a defined favicon, or any other static file (like directly opening an image) the browser is trying to load /favicon.ico as default. So far so good, but:

Your https://www.oilstainsremedy.com/favicon.ico (it’s a https URL) forwards to the http (not https!) URL
https://www.oilstainsremedy.com/wp-content/uploads/2024/10/oilstainsremedy-logo-512-1-150×150.png
which itself forwards to the https URL
https://www.oilstainsremedy.com/wp-content/uploads/2024/10/oilstainsremedy-logo-512-1-150×150.png

Check where that forwarding comes from, maybe in your .htaccess.
Or clear the favicon settings in WP, and fill it again with the https URL, since WP handles the lookup for nonexisting files like the /favicon.ico.

I set the site icon in WordPress Admin > Settings > General > Site Icon

I Uploaded a 512px square logo, I can see it in the Media section:
https://www.oilstainsremedy.com/oilstainsremedy-logo-512/
or
https://www.oilstainsremedy.com/wp-content/uploads/2024/10/oilstainsremedy-logo-512-1.png

Media section flags this image as ‘Site Icon’, i only uploaded one image file which was 512px, im not sure where th other size one has come from.

according to cloudflare settings and htaccess, all http links should be converted to https, so this should be redirected to the https version, but then it keeps redirecting:
https://www.oilstainsremedy.com/wp-content/uploads/2024/10/oilstainsremedy-logo-512-1-150×150.png

the actual files does exist and is located here:
/public_html/oilstainsremedy.com/wp-content/uploads/2024/10/oilstainsremedy-logo-512-1-150×150.png

My htaccess has this code:
#BEGIN HTTPS Redirection Plugin
<IfModule mod_rewrite.c>
RewriteEngine On
RewriteCond %{HTTP:X-Forwarded-Proto} !https
RewriteCond %{HTTPS} off
RewriteRule ^(.*)$ https://%{HTTP_HOST}%{REQUEST_URI} [L,R=301]
</IfModule>
#END HTTPS Redirection Plugin

#BEGIN WordPress
<IfModule mod_rewrite.c>
RewriteEngine On
RewriteRule .* - [E=HTTP_AUTHORIZATION:%{HTTP:Authorization}]
RewriteBase /
RewriteRule ^index.php$ - [L]
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteRule . /index.php [L]
</IfModule>
END WordPress

Your SiteURL and Home still have the URL without SSL. Change this in the backend under Settings > General. Then, if necessary, save them again under Settings > Permalinks and clear the cache from your optimization plugin “Cache Enabler”.

when i do this the site stops working

What exactly does that mean? I can currently see that the database is apparently not accessible. This has nothing to do with the changes to the domain. You would have to check whether the database access data in the wp-config.php file still corresponds to that provided by your host.