That's weird decision. In such case, i would try to run ApolloUI on Docker container which has NodeJS 9.
Sure; there are all sorts of ways to run insecure software in a 'it's probably fine' way - sandboxing, virtualization, dockerization -- with the assumption that it will even work in such a restricted scenario, as it will need access to the different files and processes to pull the information to be displayed.You're correct, Armbian 21.05 is based on EOL OS[1]. The kernel (5.10.35) has LTS support until 2026[2], but we know the developer ask you not to perform apt upgrade 
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Yeah; I'll try my best with another attempt at running it on updated nodeJS versions, but honestly it's just fine without the UI and all the benefits you get from the custom Linux install heavily outweigh missing out on the web GUI..