I’d be pretty shocked if the ad networks that spy on all of us care about RSS. You’re going to look like a bot, noise they actively try to ignore. The relevant piece of data to them would be a clickthru to the website (which they would then probably care about attributing to RSS)
You can always manually share .ics files in emails to share calendar events. I’ve never used Proton, but I’d be shocked if their calendar can’t ics export. I think that’s literally how Outlook actually implements that, so it should “just work.”