By the time I started HRT a few months ago I'd already lost about an inch of hairline at both of my temples. Shortly after starting HRT I actually began shedding and lost even more and began thinning at my crown which freaked me out but apparently that's a normal part of hair restoration. Sometimes it needs to get worse before it can get better. I can't remember the sciencey reason why though and I'm too lazy to look it up. Since then it has thickened at the crown and it's growing back at the temples and not just where it shed either. At first the hairline regrowth was just white fuzz but that's almost normal hair now and more white fuzz has appeared in what looks like a completely female hair pattern. Judging from what happened to the earlier white fuzz that may become normal hair too. *fingers crossed*
I'm not sure how much you already know about hormones and male pattern baldness (MPB) but the abridged version is that testosterone (T) converts to DHT which causes inflammation at DHT receptor sites on hair follicles causing the hair shaft to get thinner until it "dies". So to slow/stop/reverse MPB you can inhibit T production which means there will be less to convert to DHT, you can use a DHT receptor antagonist so that DHT can't reach the hair follicles or use a DHT blocker that inhibits the enzymes that convert T to DHT. Personally I take spironolactone, Avodart (dutasteride), Estrace (estradiol) and Prometrium (progesterone) which apparently covers all three methods.
Taking spiro and Estradiol together (or high doses of just estradiol) lowers T production and spiro also always acts as an DHT receptor antagonist. Avodart (dutasteride) is a DHT blocker like finasteride except it's far more effective. It may potentially have more long lasting side-effects though due to a massive half-life of 5 weeks. Prometrium is the controversial wild card but despite rumours that it may increase T (spiro helps stop P from producing T though) it hinders DHT production and pregnant women who are full of P tend to have great hair. Either way it hasn't stopped my hair from regrowing but I mostly take it to assist with breast growth.
It's my personal belief that Avodart is the single most effective drug for resisting MPB as it reportedly lowers DHT by over 90% but I'm not a medical professional so don't take my word for it. Maybe read some research papers about it and talk to a doctor or endo. You'll find that most trans women who've taken it will agree that it's very effective though.
Edit: I don't think you need to be officially diagnosed with gender dysphoria to get a prescription for Avodart but it's official use is for treating enlarged prostates and it hasn't been officially cleared as hair restoration medicine yet. If you can't get a doctor or endo to prescribe it to you then you'd have to settle for finasteride or... the black market, I guess... but I don't know anything about that at all.
