I’ll log an issue on this because the behavior changed, but I wouldn’t be surprised if it dies due to neglect.
The examples in this Tips & Tricks post use environments to control the behavior of sites that are built for online and offline viewing, enabling relativeURLs only when needed:
https://discourse.gohugo.io/t/crafting-and-configuring-a-serverless-site/48029
I also noticed that you are using canonifyURLs:
https://github.com/McShelby/hugo-theme-relearn/blob/main/exampleSite/config/_default/hugo.toml#L10-L17
See https://github.com/gohugoio/hugo/issues/4733. It’s going to happen at some point; I’d plan for it now.