this book is good, and it provides a useful glossary which is great to cite when you're working in subfields where other academics are less familiar with queer terminology and you need a quick way to explain it. it's available open-access. the editors and contributors have largely published other things too, so follow up on them and you'll find more of the recent stuff -- the list below is trending older, but here are a few other useful resources and books:
the medieval history lgbtq internet sourcebooks page. this is an older resource so it doesn't have much in the way of recently-published stuff but it does collect together some primary sources as well as older (mostly 90s) scholarship, particularly looking at the christian medieval dimension, and the site is broadly up-to-date in terms of archive links to now-defunct sites. i will note however that queer history is one area where medieval history has moved on since the 1990s, on which note:
and the john boswell page at the same site. boswell's work on "same-sex unions" from 1994 was pretty foundational to the field, but it has been developed on and it's worth reading some of those follow-ups and critiques rather than just reading him in isolation, because he was wrong about some stuff (even if maybe less wrong than his early homophobic critics thought). this page shows a lot of the earlier scholarship responding to boswell. of the cited follow-up books, halsall identifies claudia rapp's 2016 book on adelphopoiesis as the best one, and i can confirm it's a non-homophobic response to boswell that pushes back against his central thesis about the purpose of brother-making ceremonies (with extensive evidence for doing so) without denying the possibility of queer people and how they might have expressed those relationships using systems not built for them
doing unto others: sexuality in medieval europe by ruth mazo karras and katherine pierpont got a new edition in 2023, i read an older one when i started doing queer history in undergrad. probably a good starting point
constructing medieval sexuality eds. karma lochrie, peggy mccracken and james a. schultz is another one i read as an undergrad -- it's from 1997 but i remember it being pretty useful, as are other works by these people
though he's notably not great at the actual medieval history part i do think it's worth having read foucault before embarking on queer histories because so many other people will be engaging with his work and methodologies. for the same reason i think it's worth reading judith butler early on, though perhaps don't start with gender trouble -- undoing gender is more recent and more readable, and bodies that matter is also a good follow-up
here's a really useful-looking reading list with primary and secondary sources for teaching queer medieval stuff
on that list i see also bill burgwinkle's sodomy, masculinity and law in medieval literature: france and england 1050-1230, which is more literature than pure history (a lot of this stuff will be -- a lot of our sources for this kind of social/emotional history in the medieval period are literary sources) but was very useful to me when i started doing queer readings and had mostly encountered terrible scholarship from the 80s
book series like the "new queer medievalisms" series may be of interest. there are also several volumes in the "new middle ages" series that focus on queer histories, gender, etc, such as constructing gender in medieval ireland; homoeroticism and chivalry; queer love in the middle ages, etc etc
journals like journal of the history of sexuality are, unsurprisingly given the name, likely to publish relevant material
medieval lit journals like arthuriana tend to be pretty strong on the literary side of this. my own subfield of medieval celtic studies is weaker on this topic, but studia celtica fennica has a forthcoming special volume about gender and theory in celtic studies, to which some of my friends are contributing, so this is shifting
the most recent work will generally be more topic-specific and in journals, so this list is focused more on broader overviews and general interest medieval queer history stuff. the medieval period is long (1000 years) and geographically diverse, and also things like gender variance and identity vs sexual behaviour would be handled pretty differently, so it might be possible to give more detailed recommendations if you have more specific areas you want to focus on
i've been out of the queer theory game for a bit now and my background was mostly in medieval literature, so most of the recs i have are (a) a few years old and (b) more about how these ideas are represented in literature than their historical dimension, but there's some history in there -- and some of my mutuals also work on these kinds of topics, so they may have more recs to offer, particularly if you have any particular directions in mind