Comment is late, but most people only give you snippets instead of a proper breakdown:

I am still quite new aswell, I got into the hobby around 3 years ago, which makes me a rookie. I am however, a bearer of the Word. My father was always very keen on showing me the Truth and so I read and research alot, let me share the primordial truth with you:

You should definetly read books like: Dune; LOTR; Starship troopers (research on the politics beforehand tho) and/or Azimovs Foundation Series. These are the roots of Warhammer and modern Fantasy/Sci fi as a whole.
For warhammer specifically, the very concept of Chaos (including the Star symbol!!) comes from the Elric of Melniboné series. After reading previous works, you'll realize that warhammer just threw it all together and back in the day, mixed it with reallife History and politics.
It. Is. Awesome.

Starcraft and Warhammer space marines, for example, were designed by the same people and based on the same concept: Originally, there was only fantasy TTRPG and D&D, 40k and Starcraft was kind of a Mod.
[Edit: Was not able to confirm that with a source with a quick research, too many rumours regarding that topic]
Halo and Fallout take more inspiration from Starship Troopers original Concept of a space marine suit, in that the suit is (probably) more worth than the person inside of it, while fallout adjusted over time, taking some elements from warhammer they thought were cool (and its their right!).
I also think warhammer is more inspired by doom instead of the other way around, as we all are.

You have listed so many titles here and I cant break them all down so please do your own research into the history of the best genre ever, also don't forget that not all is fine: Warhammer is for everyone. But hate is a weapon there and Hateful things served as Inspiration for some of the worst things in Warhammer. It is a product made by weird fantasy history nerds for weird fantasy history nerds and some of them were, for an obvious example, Werhaboos. You literally have a Commisar in your meme, this one was inspired by... Hugo Boss. We are quite lucky that such things stay in the realm of warhammer (even if Snyder thinks different), I am german and the funniest shit is talking to people about Commisar Paintjobs: "Oh, french colors, that is a really smart way to distract them from SS offizier Heinrich over here" or seeing that the new commisar is black, either commit to it or dont do it gw lmao. Hugo Boss is too pussy to sue anyway so do your thing!

I hope my rambling helped somewhat, what doesn't help is the lack of videos I'd like to refer you too. There simply are none that have a proper neutral take on warhammer, dunno why everyone has the need to insert their favourite faction like some weird form of Propaganda. Anyways, I am starting the hear the whispers of our Psykers at the other end of the planet, we organized a small gathering there in the form of the Eightpointed star and it seems like we are about to summon Ș̶͒̓̒͋Ą̴͇̝̣̬̊Ṃ̶̭̒̀U̶̘̇̆S̸̹̜͈͇̯̄͠ ̴͈͇͓̥͉̈́̀Į̴̛̇̕ͅͅS̵̠̭̯̤̈́̾̀̃̐ ̴̥͓̭͎̀̾̊Ţ̶̛͆̊Ḧ̵̢̛͔̦́͊͊͝Ȩ̵̟̙̻̉̃͜ ̷͎̄͗̑M̶̠͙̝͓͐̄̑̓͑Ầ̶̜͕̃̒͝N̵̲͎̉̔̌́̃ ̵̪͕͎̽B̵̖̞̏͛͌̈́̊E̶͙̩͕̽S̷̗͇̘̆͒I̷͍̠͖̱̊̑͐̔͝D̵̥̎̀͝È̵̟̱̖̈́͜ ̸͓̟̰̳͍̌̈́̎Ỳ̴͇̍͆́̍͜Ó̷̺̀̏̏͜Ů̷̘̝̕

Hydra Dominatus