on android I use fossify calendar

you can also find another usefull app in their repository:

https://github.com/FossifyOrg 

 Thank you ! 

 I use proton calendar. But only makes sense, when you already use a product of proton. 

 I see, do you recommend to use proton mail ? 

 I do 

 Ok nice 👍 

 Yes I use it since around three years. And they do a great job for privacy.