This bug is probably related to MC-260598.
How to Reproduce:
Step 1. Fill a horizontal plane of blocks in the sky with any kind of banner using `/fill` (perhaps a 10 by 10 space is a good choice).
What is Expected:
Notice how rain does not pass through the plane of banners. Rain should pass through banners as they aren't solid blocks in any way.
Can confirm in 1.20