There are not a lot of choices. People in the US typically either use Google, Microsoft, Apple, or their ISP. Beyond that you have to go to a hosting provider or host your own. One of the most important things of a mail provider is that it support MTA-STS. There are many providers in the EU that do. Not many in the US. It is also important to pay for an email product, rather then be the product.
Regarding MTA-STS. Fastmail did not the last time I checked, you should check if that has change. Google does. Microsoft was testing it but I don’t know how that turned out. There are EU providers that do including Proton does support MTA-STS last time I checked.
I actually use Namecheap cpanel email. They don’t do MTA-STS but the do allow opportunistic transport encryption. Technically I should be able to configure incoming MTA-STS but I’ve not gotten it to work. Maybe just does not, or maybe I’ve not put enough effort in to do it.















Keep in mind that there is some history too. Linux was released under the GPL earlier then BSD became open source. It then developed faster and got more support. So it became the popular kernel.