Some guys here have good experiences with Text:HTML, mainly for movie credits. I personally find it way too restrictive so I use one of two ways of rendering HTML/CSS animations.
One way is to use an older version of Shotcut (v 20.07.11). I keep a separate copy of this available just to be able to use Text:HTML animations.
Another way is to use OBS studio to play the HTML as a “browser source” and record the video. In both cases I import the video clip produced back into the latest version of Shotcut.
Some just run the code in a browser and use a screen recorder like Sharex to record the animation and import the clip into Shotcut.
OBS handles newer HTML animation techniques, like 3d, better than the webkit browser that was included in the older Shotcut versions with the WebVfx framework.
See here for more details: