As is often the case there is more nuance to this. As others have pointed out, it is still possible to run your own mailserver if you really want to.

But, there are also other options that aren't google, microsoft or any other service.

I personally have registered my own domain and have my mail hosted by mailbox.org. If I am ever dissatisfied with them I can simply pick a different mail hosting provider and move my domain there. Other privacy minded providers can be found here: https://www.privacytools.io/privacy-email

And there are also more options if you just want reliable mail and care slightly less about overall privacy. Fastmail for example is a popular choice.

Yes, these are not free. But neither is hosting it yourself as that costs you the VPS/container to host it and a bunch more time and effort.

What it does provide you with is the ability to no longer use big tech while allowing you to mail with people still having their mail hosted there.