The venn diagram doesn't need to be perfectly overlapping circles. When open source is not a viable option or you need something beyond the scope of what open source offers, the next best thing is to use a product from a reputable company that has been properly audited and has not completely enshittified.

Now, whether Proton is truly that company is up for debate. The CEO has made some pretty troubling comments, but the products themselves have not devolved all that much. You can probably find better than Proton, but you can absolutely find a hell of a lot worse.