Either that time Fabious Bile was captured by the Drukhari and started experimenting on his fellow prisoners and they decided it would be more fun to let him go or that time he told the chaos gods they don't exist.
Definitely my dude. Examples are the Interex, Olamic Quietude, and technically the league of Votann are human worlds. There is one known former imperial worlds now a rebel empire called the Severan Dominate (12+ worlds are known within the Empire) that somehow still persist
Also less multi system but single planets are inside the Kronous expanse (collection of independent human worlds, notables being Vaporius, Zayth, & Seldon Folly (formerly called Pastorus). Likely more worlds are independent thanks to the great rift now
The fact that since more humans in the Tau Empire along with some other species may be accidentally creating a God of the Greater Good in the warp seems like such a cool idea I hope gets expanded on more
One of the first bits of 40K lore I was introduced to was the Blood Angel's civil war from the first Blood Angel omnibus I got after getting into 40K from the last Dawn of War 2 dlc. It was a fun story that showed how insidious chaos could be and the actual terror that fighting a lord of change was.
Also the second story from the Grey Knights omnibus I got at the same time was interesting. Its called Dark Adeptus and while it can drag, it involves the cast sneaking through an entire world taken over by the Dark Mechanics so you get to see some of that which never really shows up.
An Ogryn named Nork Deddogg once dragged a Chimera to his commander's position because his commander asked for a medikit. Nork reasoned that "Da medikit is in da carrier, sir!"
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Rylanor virusbombing Fulgrim is just way to funny to imagine too
The fact a baseline human singlehandedly bested a squad of White Scars in a training bout.
Also that a trio of Ogryns once ganged up on & beat a Genestealer Hunter to death with clubs in the back of a truck.
The human is Scout Seargent Oan Mkoll of the Tanith First-And-Only, & he lures them into a trap that'd kill him too.
"That's why the Guard always wins: we're expendable. One trooper for three post-human adversaries? That's victory."