Refresh Rate Changer - OnePlus APP
Practically it has 2 buttons that execute 2 different adb shell commands:
adb shell settings put global oneplus_screen_refresh_rate 0 or 1
Additionally it can support and help other One Plus users lock their screen refresh rate to MAX using 'Lock to MAX' option.
Open source project, you can find the code in the following repo:
https://github.com/llabropoulos/refreshRateChanger