My suggestion is simple. Follow the standards.
This shows that the bottom row should have, right to the space bar, at least AltGr (right alt) and a Control key.
Here's, in my opinion, an easy to digest graphic of what is standard in this case.
https://imgur.com/a/a4vQixT
The location D13 in the 104 key layout ("ANSI") would expectedly map to the keycode giving "\|" on a US qwerty layout.
Except for the position of right control, the 105 keys layout ("ISO") is fine in the pictures of the last blog post about the Pinebook pro.
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That said, I would add that both keyboards should present the same key at the right of right alt. Meaning that the 105 keys ("ISO") layout should also have right control there. And if impossible to change for the 105 keys ("ISO"), the 104 keys ("ANSI") layout should have the same key present, so there it would be "Delete". That is, mainly so that software fixes for the layout at the operating system level can apply equally to both layout, without surprises.
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EDIT: In addition, any complaints against a standard layout can be readily answered by "this follows the standard", which is kind of a cop-out, but has evidence backing it, while any changes compared to the standard is invitation to unexpectedness by the end-users, compared to other keyboards.