Well to me that's a different question from 'how is it going' ('going badly say Brits') - I'm not saying it's not a useful question, just different.
The full question is:
> The EU transition period ended on Dec 31st 2020. Since then, do you think Brexit has gone well or badly?
but as I commented elsewhere in this thread, compared to what? If your baseline is (as it likely is) that it is a good or not good idea at all. An answer (that the poll couldn't get) might be 'I think a better job's being done and it's going better than I thought possible, but we're in a worse place than if we'd never left'. Another might be 'we were right to leave and I stand by that but this execution is terrible'.
I just noticed there as at least a break down by leave/remain vote in the 'politics' tab: https://yougov.co.uk/topics/politics/survey-results/daily/20... - I suppose I just think that should be front and centre as the main result, it makes more sense to me (not parties so much, just the referendum vote) than 'all adults'. I think it's much more interesting. It shows exactly the bias from that that you'd expect, but also weighted towards the 'bad' end from 'leave' vote more than 'remain' is toward 'good' - which makes the same point as overall of course, I just find it more convincing.