USB ports in MacBook Air not recognising all devices

I bought a new MacBook Air (the basic model) on 14 May operating Mojave V. 10.14.5 It has 2 USB ports which had been working fine.

On 21 May, my external hard drive was plugged in to back up the Time Machine. (I plug it in every time I use the laptop from home as a matter of course.) It had been working perfectly since I got the new laptop (so about a week, updating pretty regularly) and done some backups on that day but then the message came up "disk not ejected properly", even though I hadn't ejected it, turned off the laptop, etc. (I had just been typing in Pages - very straightforward.)

Since then, neither of the USB ports will detect:

• external hard drive (also NOT showing up in disk utility)
• compact camera
• external speaker
• USB headphones (these do actually show up in System Preferences/Sound but they do not pick up input/output)

(The USB ports ARE detecting other external devices such as iPad, iPhone, Kindle, USB sticks, printer)

I have:

• checked all devices in both the ports
• tried 3 different cables across 3 devices, with no effect
• check power cables for all 3 devices - all working fine
• Googled for answers, but most come down to sorting it out in Disk Utility, but as I said, the drive isn't showing up there

I don't have another Mac I can test the devices on.

I am not technically minded, but it does seem to be a problem with one type of external connection, as the cables are interchangeable. The only thing I can think of is that there was an OS update about that time which might have caused an issue. Does anyone have any other ideas?

Thanks!