Mobile: Fossify Calendar with DavX5 as the interface (both from FDroid)
Laptop: Vivaldi's built-in Calendar
Tablets around the house: Home Assitant's calendar (I don't recall the specific integration, but it was a HACS one from memory)
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Massively offtopic and definitely over reaching, I know, but... from reading this post, as well as journalling, I'd recommend you also consider a counsellor if it's heavy life issues.
Seeing one myself has helped me a hell of a lot... I only wake at 3am due to work stress now, rather than (all the other stuff)