For each device, the key combos should be at the foot of the info page: https://doc.e.foundation/devices/starlte. From this I see.
Download :
With the device powered off - hold Volume Down + Bixby + Power.
I wrote an article which I hope answers your questions. Know your hardware - Samsung. Your first boot into TWRP (half way down the contents section) does seem quite contrary at first – do not expect Samsung to cooperate! You are fighting Samsung for control at this stage; once TWRP is installed you are in a stronger position.
Even the Easy Installer gets it wrong,