I also don't know why it disappeared when there was no apparent update. But you can use another similar function to replace it.
Solution can be found here https://pandasdoitbetter.blogspot.com/2023/12/lametric-time-mystrom.html
Even though there was no visible change, I still have no idea why it vanished. However, a comparable function can be utilized in its stead.
Rene
Why ist the mystrom app gone? This app worked fine! I need it to be able to measure my current solar production.