Driver software for a wide range of printers and scanners is installed automatically on demand — see bit.ly/prntscan. Check the hardware manufacturer’s website for new updates. Printers that support AirPrint might not need additional software. Accessories that require custom software extensions to be installed, such as Wacom tablets, Logitech mice, and some others, may have problems in High Sierra until these are updated.
If a Bluetooth device won’t work, go to System Preferences’ Bluetooth pane, put the pointer over its name, and click the X revealed to the right to disconnect the device. Now set the device to pairing mode (check its manual for how to do this); when it appears in the Bluetooth devices list on your Mac, click Pair next to it.
Printer/scanner drivers installed by macOS are updated for you, but you’ll need to check manufacturers’ sites for other types of gear.