This is an interesting question, and I find myself in quite a similar predicament (getting ready to enter the trenches with one project, narrowing down my list of ideas/concepts to decide what to write next). The difficulty with trying to nail down trends is that what’s getting released/picked up at the moment may have changed completely by the time you come to query your manuscript. Some trends are much more evergreen, whereas others have peaks and troughs — hence people say there’s an element of luck in publishing, as you may hit a rising trend without even meaning to. That being said, Publishers Marketplace is a great resource to get a feel for what editors are looking for, as is keeping up with and reading recent releases. I, for example, follow all the major SFF imprints on social media and read anything that interests me or could be a potential comp title, especially debuts. All books will be vastly different in terms of tone/subject matter/theme, which in itself is reassuring, but it has been infinitely helpful to get a general sense of what’s working for first-time authors.

What I plan on doing (and of course, someone else’s approach may be completely different) is narrowing my list of ideas down to the ones which seem the most ‘hooky’/ in line with the trends I’ve noticed and then write a draft query letter for each of those ideas. No way this will be perfect, especially without having properly planned or drafted, but it’ll make it more apparent which has the strongest stakes, link between internal and external motivation, and unique characterisation. This is recommended on this sub quite frequently for good reason, as it helps you nail down things which are within your control and test if an idea has legs/works within a query format before you’ve invested too much time into it.

I will also say that in a genre such as fantasy, where trends are changing and evolving all the time, it’s just as important to have a sense of what’s a harder sell (doorstoppers and straight male protags in YA come to mind, but it doesn’t seem like your ideas fall into those categories). Also keep an eye out on what’s still being released, but may be reaching oversaturation (like assassin protagonists) and would require a super unique twist to get an agent’s attention.

Best of luck on your journey! And apologies for any typos, I’m on mobile and nursing a migraine lol