Hey there,
and thanks for your message. I hope you’re doing well today.
The only way to find that error is to activate DEBUG Log as described here: https://wordpress.org/support/article/debugging-in-wordpress/#wp_debug_log
After activating the debug log functionality, reload the page with the white screen and check the debug.log file. You should see a “FATAL Error” anywhere. You can also post the content of the file here if you want.
1) is it possible to set conditional properties, which are only active if an ACF field exists in a post (assuming that not all fields are used in all posts)?
> Currently not (without programming knowledge)
2) is it possible to make the entire markup, e.g. for an event schema, conditional, i.e. the schema markup isn’t inserted in a post if NOT ALL of the ACF fields used in the properties have values?
> Currently not (without programming knowledge).
Hope that helps