I just installed calrs, a recent alternative to cal.diy. It absolutely rocks! The only downside is that it requires me to activate STARTTLS as force-TLS-SMTP isn't supported (I had to check the source code). It’s young, very promising, and honestly, I don't know what I could ask for more.

I also replaced Radical with rustical, and I gained free push updates.

https://cal.rs/ and https://github.com/lennart-k/rustical

And if you wanna try it out. https://cal.ache.one/u/ache