Your homemade bread likely falls in the oven due to overproofing (rising too long, weakening gluten), underkneading (not developing enough gluten structure), or an oven that isn't hot enough, preventing proper "oven spring" before the structure sets. The dough expands too much, and the gluten can't hold the gas, causing it to collapse when it hits the heat and can't support itself.
The dough rises too long and the gluten structure weakens. Three, not baking long enough. The structure hasn't set so it caves in as steam escapes and the crust can't hold the shape. Four, the oven wasn't hot enough.
Knead longer, use higher protein flour, scald the milk (180F) and that should do it. Don't have to do all but if nothing else knead longer. Recipes usually understate the amount of kneading really needed, IMO.
This is the approach The Spruce Eats recommends for bringing back stale bread — dampen under the faucet, wrap the whole loaf in foil, and reheat for 15 minutes in a 300°F oven. After that 15 minutes, the directions say to unwrap the loaf from the foil and continue baking for another 5 minutes.
Hydration: Dough that is too wet (has too much water) might not hold its shape as well, causing it to deflate easily. How to fix: Try using less water in your recipe (start with 25 grams).
The slightest knock and the carbon dioxide pockets in the loaf will push against the pushed to the limit gluten structure and the whole thing will collapse. If the dough is over proofed oven spring can't happen and the dough's structure collapses rather than springs.
Steam at the beginning of baking does a few things. For one, it keeps the outside of the loaf moist and flexible, which prevents the crust from forming before the loaf has achieved full oven spring.
Steam is being released. That steam artificially inflates your loaf. Your structural support however is lacking so as soon as your bread cools down, the gluten at work can't support it anymore so it deflates.
Use a bread box
With its dark and dry interior, a bread box helps maintain a decent balance of moisture to keep the inside of the bread soft and its exterior crusty. Make sure there is plenty of room inside for good air circulation.
Wrapped at room temperature
Aluminum foil allows for a bit more air circulation but isn't ultimately much better than plastic wrap because of how tightly it will cling to the bread. If you insist on wrapping your bread, beeswax wrap is your best bet.
It looks over proofed. It's usually after the rise falls again. You're looking for a domed top that slowly bounces back when you press on it. It'll be harder to shape when is over proofed as the dough will seem runnier and flat.
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Too much flour and not enough water can cause crumbly bread – people often do this if the dough is too sticky and they add more flour rather than kneading through it. Other culprits can be overproving or not kneading enough – the things you need to do to get a good structure.
Egg has protein, fat, water and while the fat and water soften the crumb, the protein helps with strengthening the gluten and capturing more CO2. Eggs are also helping with leavening the dough which adds to the rise. Doughs that have more egg usually rise more, so go ahead and play around a bit!
The loaf has lost its tall shoulders, and is starting to flatten. A weaker flour would have shown more of the overproofing in a flattening shape, more dense crumb, and a dense strip of small holes at the bottom of the loaf. The strong flour disguises some of the effects of overproofing.
The main things you can do to prevent your bread from falling are: not overproofing the dough, using the right type and size of pan, use the right kind of yeast, and following the recipe exactly. You may also need to lower the oven temperature and bake for longer if nothing else is helping.
If the dough feels weak and fails to smooth and hold its shape by the end of bulk fermentation, mix/knead it longer or add more sets of stretches and folds during bulk fermentation.
Too much yeast—While it seems counterintuitive, too much yeast can actually cause your bread to collapse. The yeast will make the bread rise like crazy, but later it all falls in on itself. Try decreasing yeast by ¼ to ½ teaspoon.
Dough which has risen far too long outside of the oven won't rise as much inside the oven, so your bread will be less floofy than it might have been. It'll taste fine though. It'll be less floofy, but it's not like it won't still be awesome.
The hot water pre-gelatinizes the flour's starches so they can absorb more liquid; the retained moisture prevents the bread from becoming dry or crumbly and promotes a softer texture, making it especially great for flexible breads that need to be folded, like tortillas and soft wrap bread.
If using cups, you need twice as much flour as water. Your correct measurements would be 1 cup flour to 1/2 water. This is why we strongly recommend using a kitchen scale. Water weighs more than flour so you are not adding equal amounts.