MyBB Community Forums

Hi,

Can someone tell me what theme this website is using? 
Is it a custom theme?

https://juridischforum.be/

Looks like the site is running MyBB to me

I don't think it's MyBB. The internal links are not the ones from mybb (viewtopic.php vs showthread.php)

It's phpBB, though does look more like MyBB tbf.

Its definitely phpBB, look at source code using CTRL + U, you can even see phpbb written in code