My steps prior to corruption were either one of those 4:
1) quit Nether safely, organize my belongings, enchant a diamond pickaxe with Fortune III and keep it in a chest, mount on my horse and ride it to explore the North of my village. The game corrupted as I rode my horse.
2) quit Nether safely, organize my belongings and leave to search for diamonds in my mine. The game corrupted as I was running on some hills between my base in the mine.
3) quit Nether safely, organize my belongings and leave to build a watchtower to the North of my base. The game corrupted as I was doing some earthmoving on a slope to begin placing cobblestone.
4) explore the Nether and find a Bastion Remnant, gather some of its treasures and return safely to the overworld. Upon arriving in my base, I organised my belongings in chests and went to sleep. The game corrupted as I woke up after a decent night's rest.
If I recall correctly, most, if not all of my save corruptions happened shortly or some time after returning to the overworld.
About the playing the same game on a local copy: I've tested it a few times. Although I normally experience a weird corruption seconds upon playing this local copy for the first time, once I enter the game for the second time, after this first corruption message, everything flows smoothly and i don't seem to experience any problems afterwards.
As for the "pre-corruption" copy of the world for test, I'm not sure if this will work, and I'm really sorry if it don't. I took it from my phone and transfered to my computer, but I don't have bedrock edition on my PC to verify if this is it. I'll welcome any orientation because I really want to help you solve this problem!
See if this link leads you to the "pre-corruption" copy: it should start with me on the Nether, having 40 units of cooked beef and a few diamond tools and weapons at hand:
My steps prior to corruption were either one of those 4:
1) quit Nether safely, organize my belongings, enchant a diamond pickaxe with Fortune III and keep it in a chest, mount on my horse and ride it to explore the North of my village. The game corrupted as I rode my horse.
2) quit Nether safely, organize my belongings and leave to search for diamonds in my mine. The game corrupted as I was running on some hills between my base in the mine.
3) quit Nether safely, organize my belongings and leave to build a watchtower to the North of my base. The game corrupted as I was doing some earthmoving on a slope to begin placing cobblestone.
4) explore the Nether and find a Bastion Remnant, gather some of its treasures and return safely to the overworld. Upon arriving in my base, I organised my belongings in chests and went to sleep. The game corrupted as I woke up after a decent night's rest.
If I recall correctly, most, if not all of my save corruptions happened shortly or some time after returning to the overworld.
About the playing the same game on a local copy: I've tested it a few times. Although I normally experience a weird corruption seconds upon playing this local copy for the first time, once I enter the game for the second time, after this first corruption message, everything flows smoothly and i don't seem to experience any problems afterwards.
As for the "pre-corruption" copy of the world for test, I'm not sure if this will work, and I'm really sorry if it don't. I took it from my phone and transfered to my computer, but I don't have bedrock edition on my PC to verify if this is it. I'll welcome any orientation because I really want to help you solve this problem!
See if this link leads you to the "pre-corruption" copy: it should start with me on the Nether, having 40 units of cooked beef and a few diamond tools and weapons at hand:
https://drive.google.com/file/d/1K8Z5XvWDXGUs1lNsfHUEFdrmyeTQAmhW/view?usp=sharing
As I said, I'm totally eager to help. Let me know if this link doesn't work or if you need any additional information.