The installation guides are accurate – when you can re-lock the bootloader after installing /e/ it will say so in the instructions ! On your Samsung S10 please do not attempt to lock your bootloader, the ROM is not built to be locked.
Here is a post similar yours containing several more insights: Teracube 2e Orange State at Reboot. I found it from this Search results for 'Lock bootloader after install order:latest' - /e/ community