Huawei P20 lite forgot the lock screen pin?

My brother gave me his cell phone, but it hasn't been used for a long time. Of course he forgot his lock screen password or PIN, we've tried everything possible. It is no longer listed in his Google account via Manage devices and no matter what I try (restart, recovery mode, …) nothing works. "PIN required for device restart" always appears. I already have my SIM card in, but that doesn't help, because he destroyed his SIM (from this cell phone).

https://www.hardreset.info/devices/huawei/huawei-p20-lite/