I think quite a lot of men have in-between PSA tests via their GP, not just a PSA test before seeing their oncologist / urologist. A minimum of 6 monthly would be wise or, from May 2023 onwards, 3 monthly tests (but then you have to weigh up whether 3 monthly testing is going to give you reassurance or just cause additional anxiety).
If my husband or brother was finishing HT in May, I would certainly be making sure the PSA was monitored at least 6 monthly. From May onwards, you will most likely see the PSA rising - as long as it stays below about 2.1, all is well.