If any of you want to beat Hardcore, I have tips:
Mine your house. I know this might take a while, and your house may not look as cool, but it is worth it. The coal, cobblestone, and iron you get from it is well worth it.
If you are about to embark on a journey, get a LOT of food. In hardcore, you can starve to death.
Bring a bed with you at all costs. The night can be brutal, with skeletons and creepers wandering around, so make sure to sleep at night often.
If you are being harassed by a mob then run and dig a tunnel and protect yourself. Staying in a tunnel all night is okay, as it keeps you safe.
Mind silverfish when mining. They are quite difficult to hit, they have buddies, and they can really overwhelm you. Be careful, as one death equals your world deleted.
UNLESS YOU HAVE REALLY GOOD GEAR, DON'T MINE AT DEEP RAVINES. I have already lost two runs due to these dumb ravines. Creepers will drop on you and explode on you quickly, which can be horrible. Not to mention, the ravines are narrow, so if a zombie or skeleton is chasing you, there isn't much space to go. As a result, they can easily corner you and kill you.
Craft a piece of golden armor. Don't mine gold near Piglins in the Nether. Piglins are brutal, and they have ruined one of my hardcore runs.
Get enchanted Netherite armor as soon as possible. This is hardcore, where mobs are stronger, and one death equals your entire world gone. First you get a lot of wood and food, then you mine at level 11, and you get at least 35 diamonds for all the armor and tools. Once you are done, head to the nether and go deep to find Netherite scraps. If you want bookshelves, get some ender pearls, and find the stronghold. There are a billion bookshelves for you to obtain books. You need at least 15 bookshelves to reach level 30 enchantments. My suggestion is to enchant your armor when is Netherite armor, as Netherite can give better enchantments than diamond. Building an experience farm is useful.
Leave at least two animals. Don't kill all of the animals in your land, because if you can't find any, and you are starving, you're most likely dead.
Villagers!!! Villagers are your best friend. They have a ton of fantastic trades, such as the stick to emerald trade, the ender pearl trade, and the enchanted book trade. Try getting a ton of villagers in your world. Curing a zombie villager can lower the prices.
Brew potions. I know it takes a while, but they can really make a difference, especially for tough boss fights. In your Nether trip, I recommend getting at least 21 blazerods, and a ton of nether wart and soul sand for the farm.
Build farms!!! Farms are very useful, and can provide you with solid resources.
Run away from Skeletons early on, unless you have a shield. Skeletons are insanely annoying in hardcore. Their aiming is godlike compared to Normal. They can also destroy you at full health without armor in only four hits if you are unlucky. Shields can help with skeletons tremendously.