According to Adobe's website, support for Flash will be dropped this year (2020). They advise any business or website that is currently using Flash to migrate over to a more universal platform, such as HTML5.
xat's HTML5 version of the chat and website are currently under development. By default, all xat groups use the latest HTML5 version.
Can I still use the Flash chat?
Yes, for now you can manually add "?old" at the end of a group link to use the Flash chat. For example, "xat.com/Help?old". If you wish to use the Flash version on all groups by default, you can activate this setting on the login page.