When I need a quick and easy software write blocker to triage some USB devices on Windows 10, I realized the register key "HKEY_LOCAL_MACHINE\System\CurrentControlSet\Control\StorageDevicePolicies\WriteProtect" does work on Windows 10 machine anymore.
After some researches I developed SoftWriteBlocker, it allows me to quickly enable or disable writing to all USB mass storage devices on my Windows 10 system.
Please note: I can't guarantee it's 100% forensically sound. Buy a proven USB hardware write blocker if you want to be sure.