So you’ve acknowledged the same issue, and instead of offering a solution to their issue, you decide to criticize them. They even said they’ve used Arch for 5 years. That’s not a small amount of time to be using an OS. You are what’s wrong with the Linux community, not OP.

You need to set up a DKIM record to validate your domain. If you are using proton free without your own domain, there’s nothing you can do.