Hi,
I got the same error as already written here:
viewtopic.php?p=15586231
How it looks like on the webpage you can see in the attached Snap1.jpg.
Also other forums have the same error message using the direct link, e.g.,
https://www.alpinforum.com/forum/cron.php
Thanks
RobiX
PS: I use phpBB 3.3.5 and tried it out with PHP 8.0.13 and 8.1.0
PPS: disable VigLink extension didn't change anything in a positive way