Kadence WooCommerce Email Designer Emails without HTML

Hi everyone,

I recently updated PHP to 7.3 and afterwards the Kadence Email Designer preview emails were in plain text, where they used the be HTML. When the emails are sent they are also in plain text instead of HTML. I have tried deactivating and reactivating the plugin, deleting and reinstalling the plugin and restarting Apache2, all to no avail.
I’m hesitant to edit the actual files themselves. I’m a newbie when it comes to web building, hosting and this forum.
The webserver runs on Linux, which I’m also no expert at. I have scheduled backups with tar and cron but I haven’t tested any of my backups yet. Therefore, I’d rather not back up to before the issue occured without first trying to solve the issue. Also, I won’t learn anything from deploying a back up, other than whether my backups are even working :D.
I am aware that this is not the correct place for this topic, but I can’t find the “View support forum” link to visit the theme or plugin’s individual forum.

My webserver runs on Ubuntu 18.04 LAMP, all packages are updated.
The WP version is 5.2.4 and all my plugins and themes are up-to-date.

Thanks guys
Frank van Graafeiland