Just to clarify a few points, having been up in St Andrews a fair bit over the past 6 months.
You can only play if you have booked a tee time. That can be as a single on any of the courses except for the Old where the minimum number in the ballot is two. It even applies on the Himalayas and Balgove - you have to book by phone rather than just turn up.
The official position is that no-one who hasn’t booked a tee time can play, and that’s the rule that I’ve seen imposed. There is no singles queue on the Old, or any of the other courses. If you turn up on your own without a tee time the starters will not let you join a group that does have a booking. Now, if the starters don’t see it happening (approaching a group away from the first tee for example) you might get away with it, but I have seen singles told that they can’t play even where there’s been a group wiling to let them. There may well be individual starters prepared to turn a blind eye of course but I haven’t seen it.
What they will do is allow groups with tee bookings to join up, so I’ve done that a few times with other singles or two balls with tee times next to mine.
The only other exception to this I’m aware of is that for the Old they have been taking names of people who would be interested in taking a cancellation at short notice. In that case, if someone cancels or doesn’t turn up for a time, they are putting people on their list together to make up 4 balls. I didn’t say it made much sense!
The positives have been that play has been quicker because there are a lot of 2 and 3 balls on all the courses. It’s also been relatively easy to get tee times including, anecdotally, a better chance of success in the ballot than would normally be the case at this time of year.
The changes are all temporary and I’m told that it will go back to the way it was at some point. No one I’ve spoken to seems to know when that will happen though, and it does seem strange it’s not happened yet given that most of the other Covid-related restrictions have been lifted. Hopefully it’ll all be back to normal soon.