Seconding this plea to ignore anyone telling you to force or withhold food. The whole “they’ll eat it when they’re hungry enough” may apply to many picky eaters, but if someone (kid or adult) eats an extremely limited or unusual diet like you’re describing in the comments, there is a good chance it may be ARFID. It’s an eating/feeding disorder that often goes along with autism or sensory processing disorders, but can be separate. Critically, the “tried and true” parenting strategies for breaking picky eaters will exacerbate the problem. Of course the answer also isn’t “let them eat McDonald’s all day and stop worrying,” but there are a lot of strategies for supporting someone (especially kids) to expand their list of safe foods in a low-risk high-reward way.
Like the commenter above me said, everyone who has/had ”issues with food” is going to have an entirely different list of what they can and can’t eat and a different set of strategies that worked or backfired for them. The only general advice I have that I think applies across the board is: lower the pressure. If someone only eats 2 or 5 or 10 things, every interaction with food is already very high stakes and takes up a lot of brain space. You’re probably not going to be able to make specific foods less scary, but you can make the environment safer. Never make an unsafe food the only option, don’t let them see how worried you are, don’t (like my mom did) tell them “scientists found that if you eat more than one hot dog a month you get cancer” or “if you don’t eat vegetables you’ll die before you turn 20.” And maybe counterintuitively, don’t act overly surprised or excited when they are curious about a new food, aren’t afraid of something, like a food now that they insisted they didn’t like, etc. Just go with it as a win for you both. Let them see that what happens when they can eat more food is just…they can eat more food. No drama. (Exception if they are already excited and you are following their lead.)
Resources like NEDA (in the like above) can point you toward some places to start and connect you with other parents and professionals who can offer more contextualized and specific advice. You might also look at the r/ARFID subreddit. It’s mostly adults supporting each other but there’s a lot of wisdom for concerned caregivers and loved ones as well.