Enderman can spawn on Waterlogged Slab

Do you mean top slabs? Or bottom slabs?

I'm playing on Java 1.19.1 and am having the same issue. If you have a waterlogged top slab then endermen can still spawn on it.

This report is currently missing crucial information. Please take a look at the other comments to find out what we are looking for.
If you added the required information and a moderator sees your comment, they will reopen and update the report. However, if you think your update to this report has been overlooked or you want to make sure that this report is reopened, you can contact the Mojira staff on Discord or Reddit.
_{-- I am a bot. This action was performed automatically! If you think it was incorrect, please notify us on Discord or Reddit}

@violine1101
Look at the description carefully. It's said "on the side where no water is", which means "top slab".

Resolve the ticket as a duplicate.
As MC-263395 has more details.