Can I use http/2?

[ChrisPAR]

HTTP/2 cannot be used at this time, unfortunately, as it had been causing some issues when it was enabled:

@Admin

Actually, HTTP/2 was disabled some time ago. We were seeing issues where pages with a large number of assets (like image galleries) resulted in a substantial part of those files not being loaded successfully. Also, when disabling HTTP/2, we actually saw a substantial performance increase on sites that used HTTPS.

And no, you cannot enable HTTP/2 with .htaccess codes.

If you want to know more about how that went, please see this topic: After installing free SSL certificate from Control panel, website not loading fully