Newbie Q: my title blocks run veeerrrryyyy slow

I create title and credit blocks by Open Other and select color. I take black and then hit Filter, Text Simple and add my text with the desired font
I then drag it into the timeline, title block at the beginning, credit block at the end. In both, it plays frame by frame (noticeable with a fade in as it brightens frame by frame)…then when I get to my video (1080p .MOV sourced) it speeds up to normal.
Since these text blocks are not video, I can’t change the speed.
What, please oh masters of the universe, am I doing wrong. Latest level of Shortcut (20.07.11) running under the wonderful bugginess of W10’s latest levels

Have you enabled proxy editing and display scaling?

See Proxy Editing

Is this just happening in preview or is it happening in the exported file?

Indeed. I was just about to add that this only happens in the preview. I will investigate proxy editing

As @Roger_Leitch said, you should also try Preview Scaling (display scaling)