How to make wafer paper? I would like to make wafer paper like it is used as basis for some Christmas cookies or as used in church (oblates).

This seems to be too basic to be mentioned in usual recipes. Internet search results are so much spammed by recipes using wafer paper that it appears impossible to find clear instructions on how to make the paper itself.

I found only generic instructions like "Use flour and water, maybe sugar salt. Bake."

"Use flour and water" also applies to making pizza or bread and I would prefer to avoid too much experimentation.

How do I choose the ratio between flour and water? What type of flour should I use? How long and at what temperature to bake?

I know this requires experimentation, I am mainly looking for a starting point to reduce the parameters to try.
As recipe writing is off-topic here, the starting point to reduce the parameters is to look for recipes containing "Sacramental bread recipe", "unleavened communion bread recipe", or even "edible paper recipe".

Just ensure to enclose the search items in-between double quotes (copy-paste the search terms above) and if you find a real church recipe, substitute the biblical grains like Spelt, Khorasan_wheat, ... by organic white flour without any additives if you cannot find the original easily and use a little less water.