[cynical rant – take with a bucket of salt]
you don’t
you pick something that you are competent at that pays the bills and keeps you alive and gives you enough free time to work on what you actually want to do
traditional boomer advice was to pick something you love, but after putting in endless hours of doing it over and over just to make enough to keep you fed and provide a place to sleep, you will grow to resent it with a passion – for your own mental health, you absolutely must maintain a separation between the job and your personal life