There are lots of good free resources online. Among posters here, Rob Conley has a well-regarded series of a dozen or more blogposts (
https://batintheattic.blogspot.com/2009/08/how-to-make-fantasy-sandbox.html), and Melan had a nice short "you don't need much complexity" argument last fall (
https://beyondfomalhaut.blogspot.com/2021/11/blog-hex-crawls-simple-guide.html).
http://kellri.blogspot.com/ has "CDD#4 - ENCOUNTERS" which starts off as a set of random encounter tables but then has a rather full random-hex-stocking guide stretching over a hundred pages, e.g. the Ruins table: architecture, condition, structures, contents, treasure. Graves & Tombs table: conditions, guardians, age, burial type, burial chambers, grave goods, tomb treasures...
If you're looking for *products*:
* From Judges' Guild, the Ready Ref Sheets.
* Alex Macris (Autarch; also posts here) is the author behind ACKS, and wrote the Lairs & Encounters supplement, which addresses one or two specific aspects.
* Todd Leback (Third Kingdom Games) wrote "Into the Wild" and "Filling in the Blanks"; the latter is a rather complicated high-verisimilitude system for building hexcrawls, where IIRC you can end up with each six-mile hex having its own custom random encounter table based on which monsters have lairs in other hexes nearby...