Ask anyone what the strongest block is in Minecraft that you can actually mine with a pickaxe, and most likely they will answer either obsidian, crying obsidian or netherite. All of those things take roughly 10 seconds to break with a diamond pickaxe (7 seconds in Bedrock Edition), but I bet most of you haven't heard of this block: Reinforced Deepslate. Ever since it was added in the 1.19 Wild Update, Reinforced Deepslate is the champion of the hardest block to break that isn't unbreakable. This special block is the material that makes up the center Warden Portal in the 1.19 Ancient Cities, and it is seriously tough. Completely immune to TNT, Withers and even the Ender Dragon, Reinforced Deepslate takes a whopping 81 seconds to break with an EFFICIENCY V NETHERITE PICKAXE. Unfortunately, this block is completely unobtainable in Survival, even with Silk Touch, but it is a really cool addition to the game.

Credits: I got the textures from the Official Minecraft Wiki: https://minecraft.fandom.com/wiki/Minecraft_Wiki

More info on Reinforced Deepslate: https://minecraft.fandom.com/wiki/Reinforced_Deepslate