I didn't apply to unis like Cambridge tbh because I feared I would be isolated amongst much better off people. This was in the mid 80's when far less people went to uni.
I come from a very poor background - free school meals, very few people from school going to uni (never mind Russell Group ones), etc. I was astounded at the uni I did go to that people thought they were working class or poor just because they went to a state school - even though imo some of their backgrounds were pretty well off and middle class.
I made friends fine where I did go. But even there I met students who would make assumptions. For example, the students who laughed at another student when he said he had never been to a restaurant, or who made comments about the clothes some of the poorer students had.
Now much more people go to uni I suspect in lots of circles it is seen as more normal. But when I went I heard friends from schools parents say things like only posh people go to uni and why was I going. Or even people's parents wondering how I could afford to go and being astounded that at the time there was such a thing as a grant from the government.
Of course there is the internet now so it is much easier to find out stuff. But I had never heard the term Russell Group and tbh outside of Cambridge and Oxford I had no idea what were good universities. I didn't even have the money to visit the university I did end up going to beforehand.
I do still meet families and teenagers from very poor backgrounds who don't know a lot of this stuff - although it is easier to find out now. But I think sometimes people underestimate how valuable it is knowing what is a good uni for example, or similar stuff.