Can I use the same Apple ID for multiple Macs if I only need Apple ID to update macOS? I don't use any Apple apps (iBooks, iTunes, iCloud etc). I just need to create an Apple ID to download and install macOS updates.
You can use a single Apple ID to log into a maximum of ten devices at a time (no more than five of them can be Mac).

For more information, you can refer to the Apple Support article, View and remove your associated devices in iTunes.