You thought you were losing your mind. You are not. Windows seems to have opted out of including the older HP Laser 4 and 5 from the latest Windows 10 driver updates. I have about 15 of these old work horses and enough parts and toner stocked up for another 20+ Years.
So for now there is a work around I found after three days of searching through message boards and I hope this will be of help to someone (including myself as I forget and need things written down too)
The driver is available still from Microsoft
http://download.windowsupdate.com/msdownload/update/driver/drvs/2009/07/4188_bacd1413e93b4a6362d9a2ca653c869f1c02f6f7.cab
and I have it backed up in case this doesn’t work in the future. if you need it I am sure you can figure a way to get in touch with me or download it yourself … /wind10_hpLJ5/
This extracts (thank you WinRar) into several files and I simply put them into a directory then “left clicked” the inf file and told it to INSTALL. That was it, next time I added a HP LJ5 printer it had the driver already installed.
HP has instructions hidden on their site, I found reference to it in several message boards.
https://h30434.www3.hp.com/t5/LaserJet-Printing/HP-Laserjet-5-printer-driver-for-Windows-10-ver-1803-not/td-p/6761697
it is like they knew it would be happening but didn’t let people prepare.
I am a nerd.