ssrContext variables in index.html do not seem to be working

[rtcpw]

I'm following this guide https://quasar.dev/quasar-cli-vite/developing-ssr/configuring-ssr#boot-files
Based on the documentation, I should be able to use this in my boot file:

ssrContext.someProp = 'some value';

While this throws an error in typescript, I can use @ts-ignore to get around it and compile. However, if I then do this in index.html:

<% if (ctx.mode.ssr) { %>{{ someProp }} <% } %>

I get an error complaining that someProp is not defined. Yet all that I am doing is following the documentation precisely. Perhaps the documentation is out of date and there are some new requirements that I am not meeting?