Portfolio pop up function not working

Hello everybody, first time poster here. I ran some updates today and I’ve somehow managed to disable the functionality of my image gallery. Before the updates, when you clicked on an image in my portfolio, an overlay/pop up would appear, showing the image and some information like title and description. But now it just opens the image in a new window and you have to hit the back button to get back on my site. I also have some category buttons that would only show images that match a certain category (all, backgrounds, character design or illustration), but they also stopped working.

I built this website a few years ago, with help from my brother and it’s been so long that I really can’t remember how we got it working. So, I turn to this community, searching for help. As you can probably guess from the way I described my issue, I have just about zero knowledge op wordpress, I was happy with how my site was and hope to keep it that way for a few years to come. How could I go about to get my portfolio working again? Thank you in advance for your help.

The page I need help with: [log in to see the link]