Looks like there's a bug in the a!dateField component that will cause the entire screen to go blank. (This is happening in v20.3).
a!dateField
Steps to reproduce:
1. Type a 10-digit year into any date field in the form of "yyyymmdd". For example, "20201225".
2. Tab out of the field. (You'll see an error saying it's an invalid date.)
3. Click back into the field. The page will immediately crash.
Here are the errors in the browser console:
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Interesting. I just reproduced this in a blank interface designer in 20.4, so looks like it hasn't been fixed already.