ok, thank you so much for your support..To uninstall Magisk:
1) Download uninstaller => https://github.com/topjohnwu/Magisk/releases/download/v21.0/Magisk-uninstaller-20201003.zip
2) Copy uninstaller in root of your device storage
3) Reboot to TWRP (Hold "Vol. +" and "Power" buttons simultaneously)
4) Install uninstaller in TWRP
5) Reboot your device when finished
let me ask a stupid question: so why not simply uninstall magisk from launcher?