arch

It’s unfortunately hard to convert people from WhatsApp to other software, because contacts might care to move but the group will not…

Linkace and floccus are also nice alternatives

You mean Etesync? Yes, it’s fully open source and self hostable

Mailbox and posteo are not fully open source afaik

If main focus is deliverability and encryption plus privacy

You can try with mailbox or posteo with email, and self host etesync for calendar

data-wise, OsmAnd and Organic both use OpenStreetMap so there’s no difference. I am not sure the second error in your post is a osm problem or it’s just osmand

I would say Fedora workstation if you hate the idea of getting arch-like distros but Manjaro if you just dislike the daunting procedures to get your arch work