This is my understanding of things, having been in a related situation ( I had a prostatectomy for cancer, then began HRT, but have not yet undergone any gender reassignment surgery):
An orchidectomy and oestrogen administration can reduce the volume of the prostate. Non cancerous enlargement of the prostate, common in men over 50, can cause some of the symptoms you describe. But the severity of the symptoms are not always in proportion to the degree of enlargement. I interpret this to suggest that age related prostatic changes can still occur irrespective of hormone profile. So, you may not have a grossly enlarged prostate, by virtue of oestrogen, but still have obstruction issues.
Conjecture on my part, but I imagine that a prostate from a person who has oestrogen therapy and a bilateral orchidectomy will be fibrosed. After all, it is widely reported that the (nature and ) volume of prostatic secretions is much reduced in this scenario. I suppose an MRI scan of it would need careful interpretation because it may look unusual purely from that starting point . But I don't think that anyone is trained to interpret post gender reassignment surgery prostates. All the scientific literature says, is that there is no evidence- but that 's beacuse there are no studies. But MRI is routinely used to diagnose and plan prostatectomy surgery.
A smaller prostate , likely because of gender reassignment, should make it more likely that any biopsy will pick up any tumour cells. But , as always, there are false positives and negatives.
Some prostate cancers are 'fed' by oestrogen. I was concerned about this, and asked my consultant about this before chosing to begin oestrogen for gender dysphoria. Unfortunately he didn't have any guidance. I found some research that suggested for those oestrogen dependent prostate cancers, PSA readings may be unreliable. There appears to be no routinely applied test for checking if this is relevant to an individual. When I asked if my tissues samples could be used to check, i was told not.
I've just re read what I've typed. Prostate cancer detection is enough of a lottery in pre reassignment surgery, pre HRT individuals. For trans- women, it is even more so. In your situation, I guess that's an added incentive to be assertive in any prostate related healthcare appointments you may have. I don't say that to create alarm. More to say that you will have to become your own expert. Try a 1:1 chat with the Specialist Nurses on PCUK to get you started.
Good luck, Heather.