I have now tested a number of phones with multiple ROMs. What I am seeing, specifically on phones with A/B slots, is even if I do a permanent flash of TWRP, when I flash /e/OS, the /e/ recovery flashes over the permanent TWRP flash (directions call for TWRP boot but I have tested flash) so I don’t have the TWRP backup option illustrated (or maybe TWRP was permanently flashed to the opposite slot, either way it is a clunky process). @newts also confirmed the same thing. And Here is when this happened to me. I share this because TWRP isn’t an option for those of us in this situation unless I am missing something and TWRP is still present (opposite slot?) In addition to this happening on lake (Moto G7+) it is happening on fajita (OP 6T). What other builds does this same issue exist in? No such backup options are available on LOS based recoveries are they?
As I have tested Seedvault on other OS I too was disappointed to see this has been delayed in /e/OS. I now use patchwork, apps/systems, to get everything to a new phone when moving from /e/ phone A to /e/ phone B, etesync, Mega, Signal export, etc. But still have to manually reinstall apps and web apps 
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Seedvault was much easier, export an encrypted .zip to a USB flash drive, plug into new phone, decrypt and restore. As an ex-iOS user this was the closest I have seen to the ease Apple has created with moving to a new phone.