Trying to Gain with a Fast Metabolism/ARFID

So, I made the decision a couple weeks ago to start trying to gain. I've always lurked in the community for a while now, but recently realized how much I'd like to gain myself, especially thanks to having been on estrogen for almost a year now. However, one of the issues I've always had throughout my life has been that I have an insanely fast metabolism. Like, I was literally 125lbs up until almost 2 years ago, when I started gaining weight due to muscle mass from working out a lot. Even then, it's still taken me 2 years to get to 165lbs.

Given that, I've been trying to figure out ways to gain a bunch of weight, but am not really sure what'd work best for me. I try eating as much as I possibly can whenever I can, but that really only results in maybe a pound or two over the span of 3 weeks (if I'm lucky). I recently gave mass gainer a try, and I definitely saw some results, but I feel like there has to be something that'd yield more results.

I know working out will make it so gaining is a bit slower, but I do wanna retain a decent bit of mobility. Plus, as I currently live with family, it also kind of acts as my excuse for gaining a bunch of weight. I also have ARFID, so finding foods I am able to eat has been incredibly difficult; though, depending on the thing, there's a chance my body is willing to not just straight up reject it.

I've seen a lot about heavy cream and lots of people seeing results from it, so that definitely has me curious. I also have a friend who's helped me come up with a bulking plan, so I know I can take some elements from that and use it towards gaining. But any tips and/or advice would be very welcome!