Who can help me troubleshoot my stew?

Yes, the meat will seem tough after 20 minutes, you have to let it go WAY longer than that though! What's happening in that first push of cooking is building flavor by browning the proteins so they undergo the Maillard reaction. The muscle fibers in the meat will shrink up and toughen up when that happens, but over a long period of slow, moist cooking, the collagen in between them converts to gelatin, making the fibers separate and seem more tender and juicy since they're coated with wonderful gelatin.

Have you tried stewing the meat for the amount of time it says in the recipe (usually anywhere from 1-3 HOURS)? If not, try that. If you're still having trouble, it may be that you're cooking the stew too hot, as Nancy W says. Collagen won't convert to gelatin at high temperatures.

Kenzi Lopez-Alt's advice is pretty reliable.
Here are the results of a search for "tender stew meat: https://www.seriouseats.com/search?term=tender+stew+meat and one of the articles found there for classic American stew: https://www.seriouseats.com/recipes/2016/01/all-american-beef-stew-recipe.html

Stewing will break down the colagens that hold the fibres together, but won't do much to the fibres themselves; it might help to make sure that the pieces aren't too long in the direction of the grain.

You might be boiling the meat by accident when you first start with adding the liquids. Be sure to turn the heat down quickly after adding liquids and bring to a boil then, keep the pot at a low simmer.