Male Pattern Baldness is driven by DHT. If your testosterone is sufficiently suppressed by HRT then banding should completely stop progressing and most likely start reversing to a limited extent.
I think androgen receptor blockers like Bicalutamide might be ineffective in that regard though, and you'd have to add finasteride/dutasteride to block DHT conversion. Someone with more knowledge would have to chime in. Personally I'm doing monotherapy.
If you're balding for other reasons, then HRT will most likely not stop it and you should investigate the underlying medical issue.
That said it's perfectly normal to lose a bunch of hair when brushing or in the shower. Hair continuously falls out and regrows. It should only be concerning when that amount suddenly increases a lot.
What's the context?
Some unscheduled out of spec combustion at the local refinery?