In every site/project of Laravel Forge account, there will be an SSL section where you can access it by navigating through the left sidebar.
On this page, select the "Install Existing Certificate" option and it will come up with 2 inputs which are the private key and certificate that are generated by Cloudflare.
Once you have added the website into Cloudflare, head over to the "SSL/TLS" tab and access the page that generates the SSL Certificate from the "Origin Server" sub tab. On the page press Create Certificate and another modal will appear.
Do select the 15 years validity and RSA for the private key type. Now press next and Cloudflare will generate the certificate and private key. Do copy it over to forge but do remember the order of the certificate, which comes first.
Once it's copied and pasted on Laravel Forge, do Install the Certificate and then do "activate" it so that the changes will apply. On the Cloudflare Overview page of the SSL/TLS page, you will be able to change the SSL type to Full (strict) which is the most recommended and ensure full protection.
Thank you for giving it a read and happy learning