I was equally confused where should I get the updates from. There is
http://www.onyx.com and
http://onyx-international.com Luckily I noticed that both pages point to the same Google Drive bucket.
Regarding the Russian firmware, I would extract the images to run a diff against the Onyx one. It's quite interesting. I have extracted it once, using the LineageOS tools, IIRC.
https://wiki.lineageos.org/extractin...ock-based-otas