Over the past 3 weeks after getting back into NMS after a 2 year hiatus, I started searching the forums and interwebs for how a lot of information. Info on the new game with all its updates, Freighters, Exo-Craft, mechanics and upgrades too. One topic I found most funny was how to make money quickly - some say just edit a couple of files and give it to yourself, while other say play the game. I'm the Play The Game guy and I truly discovered how to make millions extremely quickly.
Let me get to the point... all the info you read about killing monsters for their eggs, mining a specific mineral, or attacking cargo ships is all BS. That's not the way to earn Millions Quickly.

Here is is... the answer to all of your money woes - Ancient Bones.

Storm crystals are even faster, in my experience. I farmed them for about an hour and ended up with just over 30 million.

Needs to be an extreme environment planet. They only appear during storms.

Absolutely, I totally agree. It's even faster than frigate mission revenues, and it's also a good way to advance your Extreme Survival Milestone. If only I had already Exocrafts to move even faster :)

The only play that gets money faster is high-item farming, there are items woth 15 millions. If you have a big farm you are ready to make industrial production, but it's a feature you will use when you have unlocked almost everything in the game, not an early feature like Glowing Crystals.

Chances are all good sources might be not good after a new big patch. The above mentioned eggs where indeed a very good source of income. With Next (or shortly after) the value got massively nerfed.

IMO they overdid it with the price nerf; since while I previously usually spend the time gathering them (mostly) when encountering an abandoned base they are now not worth stopping by; much less looking out for.

Agreed. Although, even after NEXT, I actually found the eggs were worth it on airless planets, as you could mine them easily without triggering the swarm. But when they changed the mechanics of that so that the swarm appears even on the airless planets, it's just not worth the hassle. I fear they'll nerf the storm crystals and ancient bones though, as it's so easy to make tens of millions in a short time.

true

Or install three "S" upgrades for the scanner visor.
That raises the reward for every scanned animal to 100-300k and for every plant to ~50k.
And works on nearly every planet.

Once I learned of this method below, I know i won't try any other way to get some serious units.
Once you have few million units (made by any means you deem fit-my case Noxious planet-concentrating Nitrogen from atmosphere and then Nitrogen Salt) - and once you have a handful of Space Stations on list - empty your inventory, buy ALL Technology Modules you can get from the Station Terminal, buy more TechMods from arriving NPCs on ships, and once you're full SELL it ALL at the Station Terminal. This crashes prices down so much that we buy back the whole lot of TechMods for a fraction of price. This first step is when you lose units and need the starter pocket change.
After that go to another system, sell at Terminal = this crashes price, buy back, next system.
It's good to combine this with adding Exosuit inv slots as you'll have the cash and you need to visit as many systems as you want to be rich. Billion in an hour is no problem.

An early game method I used for making credits was Chlorine. I found a beautiful planet with rocks that gave salt underwater, built a small base, set up a medium refiner, converted the salt to chlorine, then mixed that with oxygen for more chlorine. My base had a landing pad for visiting traders whom I sold the excess chlorine to for decent profits. I also had an oxygen collector and a second medium refiner to mix oxygen with condensed carbon so I'd never have to gather fuel for the oxygen refiner.

I don't know if this is 'a lot' of money, but as I don't tend to research these things and found all this out by accident, I was quite happy with myself. This was long before I discovered a planet with Ancient Bones, which now I've got a small base on that planet with a teleporter and a land vehicle for roaming around and gathering when I need quick cash.

At this point, I mostly explore with my freighter and let my frigates collect credits for me.

I recently got back into the game and my current method for making money is trading. It can take a little bit of time to find systems with good buy/sell and wealth, but that's also part of the fun for me. After you find the systems and setup portals I can make 20+ million in about 10 minutes. The biggest downside is that you have to wait for the systems to replenish their supplies but if you have multiple trade routes that can help.

This spreadsheet helps show the trading routes. I used this guide to understand how the process works.

One downside to this approach is that you need a decent sized hauler and some decent starting money to get going. When I start my new Beyond save I'll probably try to start get units with ancient bones until I have enough to buy a hauler and start trading.