The first thing I'll say is this: it's worth it. If you want HRT, it's worth the awkwardness. Besides that for me personally, there were a couple notable things. For a couple years at the start of my transition, I had essentially no libedo (having previously had a high one) because my testosterone levels dropped too low. Mine was below detectable levels, whereas about 0.8-0.9 was a more reasonable target for me. That is to say, watch out for low energy and libedo, women need testosterone too.

Aside from that, I wouldn't say I've had to "relearn" anything, but it has changed my relationship with my body. I like my body more than ever, and certain areas are more sensitive to stimulation than they were before. It's great, I have whole new areas of my body I can enjoy in bed. On the other hand, as the dysphoria around the rest of my body has improved, my dysphoria around genitals has become more pronounced. It's manageable, it's something I had to learn to navigate and communicate to partners. HRT also commonly causes ED, but that's nothing some Viagra can't fix.

It also didn't change my interests (although they continued to develop), but it did change the quality of my attraction. Before it was aggressive when I was turned on, now it has a more slow burning desire to it. I want a build up and some foreplay leading in to it. It's not a change in interest or skill, but you could call it a shift if you like.

Also I look way hotter as a woman than I ever did as a man, so jot that down.

So I'm not a very sexual person, just saying that up front. My libido is very low and has always been that way, even as a teenager. For me, sex always felt very awkward when I still thought I was a man. It kinda worked, but I always liked giving oral to my gf more than anything because I felt like her being happy was way more important than me being happy. I had trouble staying hard a lot. In hindsight, I'm pretty sure that was because I didn't feel comfortable performing as a man during sex.

Now, after 19 months on HRT (pre-op), I can't get hard at all without a magic wand, so penetrating someone is quite unrealistic. But I also wouldn't want to. I do however like performing a more feminine role and like receiving oral more than I did before, even if I often don't cum from it. I just feel way better and more comfortable in my body.

All in all, for me personally(!), sex is such a small part of life that I would never ever delay a transition because of it.

Hi! So ymmv, but this was my experience.

I also had taken years to become more comfortable with sex, prior to starting hrt. I have been on hrt now for almost a year, and things have changed a lot.

however

The changes were all things that I was able to clearly communicate to my partner, which made it easier for her. I wasn't confused, just knew that my body appreciates a different approach now.
I would say that I started from an "okay" place, sexually. Now I am very confident and comfortable.

My libido took a dive initially, but is now up to a level I am happy with. I think it's improved since I feel more desirable now. I don't worry anymore, "ugh, why would anyone want to have sex with that," when I look in the mirror.

You've gotten a few helpful replies, so I'm going to respond in a slightly different way. My favorite poem, by Alastair Reid, discovered long before I accepted my gender identity but which carries more weight every day I live in the present:

Curiosity

may have killed the cat; more likely the cat was just unlucky, or else curious to see what death was like, having no cause to go on licking paws, or fathering litter on litter of kittens, predictably.

Nevertheless, to be curious is dangerous enough. To distrust what is always said, what seems to ask odd questions, interfere in dreams, leave home, smell rats, have hunches do not endear cats to those doggy circles where well-smelt baskets, suitable wives, good lunches are the order of things, and where prevails much wagging of incurious heads and tails.

Face it. Curiosity will not cause us to die-- only lack of it will. Never to want to see the other side of the hill or that improbable country where living is an idyll (although a probable hell) would kill us all. Only the curious have, if they live, a tale worth telling at all.

Dogs say cats love too much, are irresponsible, are changeable, marry too many wives, desert their children, chill all dinner tables with tales of their nine lives. Well, they are lucky. Let them be nine-lived and contradictory, curious enough to change, prepared to pay the cat price, which is to die and die again and again, each time with no less pain. A cat minority of one is all that can be counted on to tell the truth. And what cats have to tell on each return from hell is this: that dying is what the living do, that dying is what the loving do, and that dead dogs are those who do not know that dying is what, to live, each has to do.

It's either worth it or it's not: sexual drive or physical appearance or anything else has nothing to do with it. And that fucking sucks, but it's true. For me, 3 years in at 30+ years old, there's no other choice. It's all worth it and I'm thrilled for every day I get to live as my truest self.