I normally use FireFox, not a big fan of either Safari, Edge, or Chrome for that matter.
However, I have disabled blocking and tracking for this site, so it is a bit strange I still do not see any images.
If images aren't visible with some browsers and not with others, even with blockers off, it may be that your installation of phpBB requires some finetuning indeed, either on the phpBB-side, or server-side.
I don't know phpBB at all, to be very honest, as I only intensively have used and still am using Invision Community Suite (since 2004) for the biggest hobby site of its kind in the world, but we are also storing images on our own server. Our users may use our own server or externally host their iamges, although from a security PoV we prefer people to upload their images to our own server. It also means we're not dependent on some external host going down or out of business suddenly, with images disappearing all over the place .
I will check to see with which browser images do becoem visible, and report back. I'll do so in the report topic, so as not to take up any further off-topic space here.
Kindest regards, Wim