For me the significant markers of committed relationships were first moving in together, then perhaps buying a home together (in those places where that was still affordable), and then for those that wanted them and by far the most important having children together.
Many of my friends and family have gotten married along the way too but it never felt like a big deal because by the point they got married they'd already been together for several years. It was a nice opportunity for a celebration! But having children together seems the far greater commitment. Marriages may end but even if you split up you'll still be parents together.
I grew up in a far less religious society than the US so maybe this just reflects a different cultural background. The US has always been more religious than Europe while also having far higher rates of teen births and children living in single parent households. But US rates of religious identification and teen births have both been falling rapidly over the past couple of decades.