I moved to the US because the earning potential as a software engineer is simply so much higher than anywhere else, it's ridiculous. Compared to Australia in particular where up until 2003 or so the standard of living was exceedingly high. But now the cost of living in Australia, particularly in local earning potential terms, is actually awful.
So, Europe. I lived in 3 places (the UK, Switzerland, Germany). All of these places are different and that's the first thing you should know. The UK isn't Italy. Spain isn't Estonia. Many non-Americans have this view that the US is all one place. Anyone who lives here knows that's not true. LA isn't Omaha. NYC isn't Kansas. Europe is no different. In some ways this gap is even wider because there are many language barriers too.
The UK is a hybrid between continental Europe and the US. I found working there to be horrible. High cost of living, low (compared to the US) earning potential and the whole tech recruitment industry there is the worst I've ever experienced. I lived in London in the early 2000s and it was expensive then. It's like 2-3x that now. Unreal.
Even somewhere like Germany isn't homogenous. NRW isn't Bavaria which isn't Berlin or the former East.
I'd say the biggest thing is this: in the US there is a pervasive fear that your entire existence could be wiped out. Worse, many feel like many others actively seek this destruction. Obviously healthcare is one cause here but I think it goes deeper. America, particularly Corporate America, is very dog eat dog. Tech is a little better than this but not by much.
I'd say this is partially true in the UK but less so in continental Europe. Like I never found anyone questioning your "loyalty" to the company (for example) if you took a vacation. it was actually expected. There was less of people telling you how to live your life and feeling like you were telling them how to live theirs.
Don't get me wrong: there are rules you need to live by, more than most Americans will be used to (eg you'll be in for a shock when you try and figure out where, when and how to recycle anything in Switzerland or Germany).
The best way I can describe this is that the default position for anything in the US, the UK and Australia is you can do whatever you want unless it's expressly forbidden. Continental Europe is the opposite: you're only allowed to do what's expressly allowed. This makes society function but many Americans will chafe against this.
Houses and apartments will be way smaller in Europe than Americans are used to. You will need to use public transportation. If you try and drive everywhere then unless you live somewhere rural you will have a bad time. Many European city-dwellers get by just fine with no car at all.
If you have kids they won't have to do active shooter drills in schools. That's a uniquely American problem.
What you gain by living in any under culture is you realize how many of the things you believe aren't universal. They're just arbitrarily chosen norms. This can apply to the smallest of things like when you can go shopping and what sort of shop you need to find something (eg alcohol is only sold in selection locations in Australia but in the UK every supermarket and off-license will sell it).
What you should gain is some perspective that working like a dog because you need that health insurance and you've decided you need to save $500,000 per child to put them through college isn't universal. It's not even normal.
As far as social aspects go, this varies a lot. For example, I found the Swiss Germans to be extremely aloof (to non-Swiss). I found Germans (at least in the northwest) to be incredibly friendly. The UK is a mixed bag. London in s rat race and you'll be judged on what you have way more than most other places. Londoners will reduce you to the postcode you live in (eg "she's so SW7").
The distances are really small. You can get really far really quickly. This doesn't really apply to the UK because the airports are awful. In Zurich by comparison I left work at 5:10 for a 6pm flight once and was at my destination by 7:30.
In this era where remote work is growing, particularly if you're in tech, it's a good time to try it and see what you think.