Alwaff5 I flashed a pendrive by my OTG adapter and need to eject safely, but no instruction that I read online works for me and I really don't want to risk.
If you are using GrapheneOS, when a USB storage device is active there is a notification which has an "Eject" button. Also, in the Files app, the "hamburger menu" should show all storage devices near the bottom, and if a USB storage device is mounted there should be an eject icon next to it.
Or you could press and hold the power button and select "Power off"; when the device is off it is safe to unplug a USB storage device.
If further help is needed, it would be best to describe what you tried and how it didn't work, as opposed to reporting that nothing you've found online helps (because we don't know what you might have found online and what might have gone wrong when it was tried).