I saw this on FB yesterday (and 50 others similar), but here's the YT version. (I probably wouldn't just use CA glue, but that's just me)
One of the key bits is that the stop that holds the jig square is (like in the video above) cut off by the saw itself so that the cut edge is also a guide of exactly where the blade will be cutting so you can line up your cut-line with the edge of that stop.
I've seen several variations.
I saw one that was basically just a T-square where the long bit was a wide-ish (looked like 4" wide) plywood (more dimensionally stable) connected with 4 screws. That version is probably best for long rip cuts that are 4' or longer.
For the models with the triangle, I assume those would be built smallish (less than 12" or maybe 16" for crosscut).
I saw a few where the triangular bit was an isosceles triangle so that the jig can be use for 90º or 45º cuts which is convenient.
I saw some where the triangle was cut from one piece of plywood which probably adds more rigidity and makes it easier to build.
One of the nice changes that I saw had the base of the triangle where the stop was cut with a slot that you could put a quick clamp in to hold the guide for you (something like this)
I saw one similar where the saw was set at 45º so it could be used for bevel cuts which is cool, but something that I hardly ever do.
I saw some fancier versions where the triangle was adjustable which is great, but I like the fixed, guaranteed square cut from a non-adjustable version.
I also saw one or two where the thing was made like a track saw, one long piece of plywood with a narrow fence attached where the edge of the plywood was cutoff by the circular saw which allows the saw to slide on the jig, and the bottom of the jig supports the top of the wood being cut for a cleaner edge, especially on plywood.
Of course, I don't think that any of these would help if you'd built a deck, and needed to cut all of the ends of the deck boards straight after the fact. But they would help with many/most other crosscuts or long rip cuts.