Working on Exynos S10 oneui 3.0
If you need to enter recovery/Twrp mode on your Samsung handset and on oneui 3.0 then you are going to need a PC 🙂
Turn off, or plug in the handset into PC, press and hold power, bixby & volume up to enter the recovery menu
If the bootloader is unlocked you can wait until the warning screen flashes then quickly let go of power keep holding bixby and volume up until your Samsung boots into Twrp , proceed with flashing, etc.
If you're having trouble, try holding power, bixby, volume down until the phone vibrates, quickly release volume down and hold volume up 👍