Is the Bigfoot fascination a uniquely American thing?

No. Bigfoot could be called other names.
Like for example:
The yeti, abominable snowman, saskquach

My explanation for why we haven’t captured one is that Bigfoot is a space alien that comes and goes to the Earth on his vacation time.

It’s definitely a thing in other countries. I don’t believe they exist any more than I believe the earth is flat.

https://www.pararational.com/other-names-for-bigfoot/

I checked the link in @smudges‘s response and ctrl + F for Vietnamese. The result is “người rừng”, meaning that there is an interest in Bigfoot in my country right? No, the translation of Bigfoot is actually a misunderstanding. While Americans think of Bigfoot as a specific kind of mysterious one-of-a-kind entity that hides deep in the jungle waiting to be discovered, the Vietnamese term covers any unexplained person/entity that supposedly live in the jungle. In fact, a quick Google search shows me a real-life “người rừng”, a real person with an eccentric lifestyle.

There doesn’t seem to be any true Vietnamese equivalent of Bigfoot, nor any real interest in it. So no, Bigfoot isn’t a big fascination here as far as I’m concerned.

I don’t know if people outside the US (and possibly Canada) worry about Bigfoot. However Yetis (abominable snowmen) is the legend in the Himalayans. Australia has its Yowies. It seems odd to me that three very similar legends would pop up half way around the world, on different continents, and the descriptions would be so close. And all of these were from indigenous tribes that had zero contact with one another.

I don’t know if they exist or not. I will say it is possible. The areas all these creatures are said to exist in are very remote. It’s amazing how well animals can become invisible in the wild. Many years ago I visited Presque Isle in PA (by Erie). It is a little peninsula that sticks out into Lake Erie. It is about 5 miles long and a few hundred feet wide for most of it. The thickest part is probably no more than a mile and a half wide. We drove this isle to check it out and it was beautiful. But a few months later the DNR planned a deer hunt for the isle, issuing 40,000 deer tags. They were concerned about overpopulation of deer resulting in the deer starving. Odd thing though, we didn’t see a single deer when we were on there. If there were 40,000 deer that needed to be culled, you’d think they be everywhere. But they hide well. It might be a similar effect with the Bigfoot creatures, if they exist.

That’s like asking if Loch Ness monster interest is just a Scottish thing. People all over the world have varying interests in the North American Bigfoot/Sasquatch myth, but everyone knows that to really investigate them, you look for them in North America.

Of course since we have so much wilderness here there are countless people who grow up with a fascination of the creatures that could be out there, so I don’t doubt interest is most strong in North America, but there are silly people everywhere.