Back when I identified as a trans man I also struggled with the idea of me topping someone else in sex. Essentially I was appalled by the idea of me "being the one in control" cause I'm a major sub with not a dom bone in my body. I don't know if that's something you relate to or if you differentiate the terms top/bottom from the terms dom/sub or if they more so go together for you. I'm not talking about bdsm now but just in general who's taking initiatives in bed and who's more of the follower.
Just a disclaimer first, that my language might be a little crude and at times feminine. Cause it's difficult for me to talk about parts like ours in a completely neutral way cause you're a trans guy and I'm a detrans woman (I've been on T) so it's a little tricky to be equally considerate to both, but I try. Cause I don't feel comfortable using neutral or masculine words for my own parts, but the feminine words I use I'm not applying to your parts. I hope that's an okay approach.
I'm also bisexual and I struggled hard to see myself dating women as a trans guy who never tops, cause I also refused to see me being with a woman as "lesbian" so I couldn't solve that issue in my head back then. (But sidenote I realised I'm not a trans guy and had heaps of internalised lesbophobia, and having solved most of that now I don't have any issue with the idea of having "lesbian sex" now as a sub/bottom woman, however now I also am curious if I'd like topping women as a woman myself, but that's off topic. Let's just focus on how I handled things when I identified as male). However you didn't mention if your struggles with topping is also applicable to women or other genders than cis men, or if it's just in regards to cis men. That might be important for you to look into if you haven't already.
I was also comfortable with bottoming for cis men and took a "use what I've got" approach. My genital dysphoric feelings were fluctuating between moderate and severe, and on the moderate days I could enjoy sex just fine but it required quite a bit of disassociating etc. (I no longer have any dysphoric feelings, but that's how it was back then for me). It is surely a practical approach! However I was also curious about topping cis men and I think I only really wanted to try it because it was so often talked about by other trans men. I think I felt a mix of being inspired to try and pressured to try. However I never really did. Except from that I rimmed a couple of guys (and I fingered another trans guy, but yeah that's a little different I guess).
But also about your partner's anal issues, that sounds a little strange to me, as someone who's experienced with receiving anal penetration and having practiced getting used to it and being able to take bigger sizes over time, etc. It's not a smooth ride to get used to it (pardon the pun), sometimes I ran into roadblocks and had issues with making it work, my body having random complaints, etc. I mean I use both my holes, and the backdoor is a lot trickier. There's not much difference between afab's and amab's butts (except from the prostate) so my experiences with it can be applied to cis men pretty much just the same. Usually the biggest issue with that not working are not being relaxed enough, not using enough lube, and also not being patient enough and trying to rush it will result in pain and tensing up which causes more pain. And all of those are very common beginner mistakes to make. But if neither of those things is the issue, I'd wonder if your partner maybe has some medical issue that might be worth looking into.
But that aside, I got an idea of something you could maybe try, although it might be a little strange. If you CAN use your fingers on him, maybe just a pinky finger with lots of lube. Maybe you could then hold your hand very close to your genitals and use that finger as though it was you dick to penetrate him with, while also moving your hips to thrust etc. I haven't tried that myself so I don't know if it could work. But I can imagine it actually might, also with the bonis you'd feel everything and no toys involved. But I can't stress it enough to use use lube! Actual lube, not saliva.
About using your growth to penetrate with, I couldn't with mine but then it didn't get very big/long and the other stuff on my vulva were in the way for it to work, cause that's just how nature designed my parts. Although SOME guys can penetrate with theirs. A big "however" on that point though: it's much more difficult to manage anal penetration with it (compared to vaginal penetration) cause of it not getting as rigid as cis penises when erect and the anal opening being surrounded by strong muscles. Still not impossible though so if you want to of course you can try it! Just... try to not get too disappointed if it doesn't work.
But also please don't beat yourself up for it if you don't really feel like you'd enjoy topping. It's okay to only bottom if that's what works for you. Your gender doesn't have all that much to do with it, as there are plenty of cis men who only bottom, and also I'm sure there are plenty of cis women who never like to bottom. Only try it if you think you may actually enjoy it or if it feels worth it to give it a try. Don't pressure yourself to fit in with the general trans guy crowd, cause every trans guy is an individual like everyone else.
