I am aware this comes from a competitor and they want to go all out. However, what is unclear to me, does this also happen to paying users?

For my small business I use Office 365 Business Essentials, whatever it's called now, the cheapest one. Been using it for many years and for the price/features, it's pretty unbeatable. I use the new Outlook on my workstation since a few months, it's pretty slow and not feature complete but was ok. I'm in the EU and haven't been prompted with that window where it talks about advertisers. Will check Monday if I see a list of advertisers but I think for paid users it's not the same.

For personal mail, I use Thunderbird, I even donated to them. I like it but would have been great if it had a view like Outlook. At the moment it has table view and cards view. Wish the cards view would more customizable.