You should really use rsync instead of scp. Or if you want some syncing automation, use syncthing, it's very easy to setup.

Your choices over messaging apps are a bit all over the place. You need to meet people where they are, otherwise you'll talk to no one. What you can have is a ranking of preferences.

I could nit pick more, but most picks are solid! 

 Rsync is whole software , not 1 file to send someone.   Syncthing is good for among your PCs, again not sending someone 1 file 

 What do you mean with "whole software"?
You can and should use rsync to send just 1 file, the command syntax is exactly the same. rsync is a drop-in replacement for scp. scp is just objectively worse in every way. 

 Oh ok thanks. I'm happy you spoke up. I thought rsync was just like timeshift for whole disc backup