I have posted about this on func_msgboard and someone said that @Spirit was the most recent person hosting insideqc. It's odd because it seems like a bug fetching the content of the first post. Some threads have the white blank page, but second page works.
I wonder if it is some encoding issue that causes PHP to fart and not parse the contents of the first post, leading to the fatal error (and thus the blank screen). I would be glad to help in trying to debug this or restore data from forum database dumps, if they exist.
the data should be in the database, the error suggests its just phpBB failing to show the content (by trying to use removed php functions).
it appears to be running phpBB 3.3.13 according to the CHANGELOG.html page, so php 8 shouldn’t be an issue. i think the server runs php 8.3 which should be supported by phpbb.
maybe it is indeed an encoding issue? or something with an extension? or the custom theme? a botched upgrade?