After seeing/after hearing

Yes, it's fine. I'd prefer a comma after "this", and personally I'd put a comma after "that" too. I'm afraid that, after seeing this, other countries might follow suit.

https://www.reddit.com/r/EnglishLearning/s/NXf0sfnVwe

Yes it can. Because the parenthetical is an optional insert in that same phrase. The parenthetical replaces “after seeing this” with “after seeing them do this” in this sense. While no you can’t replace the “after seeing this” with “or after them seeing this” in a literal sense you can replace “after seeing this” with “after them seeing this” which is what this is implying. Remember anything in a parenthetical is optional information that is there often to acknowledge something that maybe is important per se but not necessary to the understanding of the sentence. As for the second it also can because all you’re doing is re-ordering the clauses. It’s actually “[clause b], [clause a]” rather than “[clause a] so [clause b]” this is because there’s more weight placed on clause b because the clarifying information provided by it is more important. This is common in argument. If clarifying info is more important it is often said before any generally known information simply to make it clear what is actually being argued. This example is only applicable if the order of the actions are important but if information is important it is almost always said first in clear English because it has to be. The second sentence is a textbook example of how a sentence might get rephrased to imply such a thing