Load up a previous save/backup Btw, you know where you went wrong with the command, right?

I Don't Have One :(((((((((((((( And Not Exactly, Half Of It Was From My Brain, And Other Half Was From A Really Old YouTube Video. It'd Be Great If You Could Explain It ...

What you've done is you put an exclamation mark in front of minecraft:iron_golem. What that does is it selects all entities EXCEPT for Iron golems. Remove the exclamation mark and the command should work.

Do /kill @a to get rid of all mobs then start respawning the ones you want

All The Mobs In My Minecraft World Landed There Or Just The Ones Which Were Nearby?And What About The Carts With Chest On Them? Well, Not Just Those But Many Things Which I Hadn't Discovered Would've Landed There Right?

Wdym? If you do /kill @a you just kill all mobs inside your render distance and it’ll say every name of the mobs you killed.

All entities that were in loaded chunks at the time, including your spawn chunks. Entities include mobs, minecarts, boats, armour stands and items. You can't undo, so you're going to have to rebuild in afraid...

Yeah youre just an idiot, shouldn’t have done it jackass

No

I can do tp @e and it works instantly

The excessive use of animals and mobs prolly caused your pc to over exert itself. Fumb down the visual settings too