Hey MIZMU, changing the day of the week is not supported at the moment, but it might be possible to integrate that in the future. I’m not sure if I’ll have to time to work on it, but I’ll keep it in mind for future feature expansion rounds. To keep track of the progress on development, please feel free to subscribe to this feature request: Choose the starting day of the week · Issue #118 · glutanimate/review-heatmap · GitHub
Hi there! The congrats page (which is the page you see when finishing a deck) was overhauled recently-ish on Anki’s side (around Anki 2.1.38) and so far I sadly haven’t had time to add support for the new page. But this is definitely up there in terms of priority and will likely land in the next version of Review Heatmap (which will release later this year).