Power off the device, and boot it into download mode.
With the device powered off, plug in the device while holding Volume up + Volume Down + Power.
For me, I have been unable to access Download mode, the tablet boots up normally !
To access the Download Mode, I’ve used adb reboot bootloader or, with the device powered off, plug in the device while holding Volume up + Power and choose Reboot to bootloader.
BUT I have never seen the onscren instructions coorelate to “Continue” and/or “Unlock Bootloader”.
This was an issue for me. You have to both, unlock the bootloader from the menu within the bootloader as per the lineageOS “pre-install” instructions and unlock the bootloader from the developer menu afterwards.
Also I found that you have to keep unlocking the bootloader everytime it reboots into official firmware. Otherwise it keeps… relocking? It will also overwrite recovery every reboot as well as long as it’s running official firmware.
I also had difficulty finding the bootloader unlock from the developer menu, until I found out Samsung hides the option until the device has been online for seven days. You can player with the date/time settings to trick it that this has passed. I mentioned this over in the S5e documentation thread, along with a link to the instructions: Samsung - Galaxy Tab S5e (Wi-Fi) - gts4lvwifi - Documentation Suggestions
Timing on this was kind of a bitch. It will also ONLY go into download mode if it reads a data connection to a PC via USB at the same time. Hooking it up to a charger and holding those buttons will not be sufficient to boot it into download mode.
It was challenging to flash. Works like a dream once you jump through all the hoops though.
I never had that problem but another option would be to do a “adb push e-0.17-q-20210529117214-dev-gts4lvwifi.zip /sdcard/” after you wipe/format the various partitions. And then use TWRP to flash the .zip file.