They are very similar phrases. I think saying “all of this” sort of views the object of the sentence holistically, whereas “all of these” focuses on multiple individual objects. For example, in the first sentence, I would picture an example like somebody showing another person their house renovation. A renovation involves a lot of things changing, so they might say “all of this”. But for “all of these”, I would picture somebody showing another person multiple distinct and separate objects, like paintings.

Hey, yeah those two sound almost exactly the same. Basically, use "all this" when you’re talking about a situation or a big group of stuff that feels like one thing. For example, if you walk into someone's house and they have a whole new setup, you’d say, "How did you afford all this?" It’s like saying "all this stuff." Use "all these" only when you are talking about specific, separate items you can count. So, if your friend is holding five new iPhones, you’d ask, "How did you afford all these?" because you’re looking at the individual phones. If you’re ever unsure, just use "all this", it usually sounds more natural in a general way.