How does LibreELEC solve, that there is actually no 64-Bit Widewine for arm chips
ChromeOS started shipping a 64-bit update image that we could extract 64-bit widevine libs from about two years ago, hence we switched all 64-bit ARM SoC hardware to "aarch64" for LE12 as there was no longer a need to force "arm" userspace.
So we do exactly nothing and inputstream.helper picks the correct version to use; except in your case where some upstream bug has resulted in it installing a 32-bit lib instead of 64-bit, which is not arch compatible and results in errors.
NB: I'm not entirely sure how to reword your too-long and incorrect thread title, but I'll have a go.