It looks like all the old files are still hosted on the server. You can just replace the version number in the download links with one of the tags from https://git.zx2c4.com/wireguard-windows.
adb shell settings put global package_verifier_user_consent -1
This does not require root access and prevents Android from invoking Play Protect in the first place. (This is what AOSP's own test suite does, along with other test suites in eg. Unreal Engine, etc.)