At that point, you can also categorize them by flash drive, i.e. "Medical" will be a drive full of ZIM files and instructions to download Kiwix. A person walks in, they get a drive, and a week later they can return it. Month, if you're generous.
That's gonna present its own security issues. A person could overwrite the data with something bad, or change drives with a rubber ducky, what do I know what kids are up to these days. A way to make the drives read-only might prevent some of these issues, but a "sanity check" upon return may give you info if the drive has been tampered with. If everything is the same, you're okay.
Bring-your-own-drive schemes might work too, if a person can connect to some NAS and download what they need to their own drive. That might prevent people messing with the data. If you want a surefire way, DVDs are not dead yet (contrary to popular belief). Then, you could theoretically get DVD readers pluggable via USB, hand those out. It'd be easier to keep track of those this way, so a person can go "I'd like that one DVD you have," or "Can I get a copy of all things medical with a reader to go with that?" This will be more inventory, but a lower chance that you'll hand out an infected drive to the next person.
Honestly, then we can get into people returning discs they didn't get from you or infecting entire discs, but a DVD is dirt-cheap (if you buy bulk, it can be even cheaper,) and then you are only limited by the amount of readers.
SD and microSD cards are too easy to misplace or lose, so I'm not really counting those, but having a writer for someone who brings their own media would be a way to spread knowledge. A 21st century printing press, but for DVDs, SD cards and stuff.
Update, mid-writing: there are HDDs and SSDs that are meant to be WORM (write-once, read many). These would be an option, but I'd go for more expensive SSDs rather than spinning rust. I've seen the state of library books :-D