This guide is inspired by the other guide:
Make 100,000,000 units every 3 hours mining activated indium By ʟǟֆȶʟɨʋɨռɢքօɛȶ

It is very well made, and I just want to provide the method that I personally uses.

One of the quickest way I know how to make money involves salvaging sentinel ships , or sentinel interceptors. I approximate that, after some practice and set up, this method can generate around 100 million credits per hour. (One ship yielding 20 million credit, 12 minutes of combat and restoring the ship). Currently, the value of sentinel ships is quite busted, and it is unlikely going to be nerfed, given that the value, to my knowledge, is relatively untouched since the update that introduced them.

In order to locate a sentinel interceptor, one must either acquire a Carrier AI fragment, or an echo locator. I personally found the Carrier AI fragment to more more easily obtainable.

In order to obtain an Carrier AI fragment, one must have a level 5 wanted level (in space). You can easily get a level 1 wanted level by shooting at the space station with your ship's weapon, thereby initiating the first wave of enemies. Defeating all 5 waves will reward you with a Carrier AI fragment

Note: While it might seem daunting at first, the sentinel capital ship is easier than it seems. I would suggest that, before the fight, you stock up on either starship batteries, or a phase beam. shown below. (credit to the NMS wiki for the images)
















The starship battery is very cheap, costing gold and tritium, which is easily farmable. The phase beam might require some installation. For new players, I would advise around 10 starship batteries per fight, for the minimum. Simply unload your weapon at the mothership during wave 5 to destroy it quickly. Just remember to recharge your shield. To unlock the blueprint of these materials, simply find them in the space anomaly. Once you have enough credits, you can simply purchase the materials of these items in mass

Alternatively, if you want to cheese the fight, I found that you can camp at the tail exhaust of the capital ship. By doing so, only the spawned interceptors can attack you.

At this phase, you can activate the AI fragment and follow the mission to get your sentinel ship. All of the steps will be given out by the mission.

Some tips:

During one part of the restoration process, inverted mirrors are required. You can just snipe the tower from far away with whatever means necessary, and then run away. The swarm will easily de agro after a while.

I suggest that, during this process, you should harvest massive amounts of radiant shards (the purple crystal requiring advanced laser to mine), as well as inverted mirrors. By doing it in mass, you can save time salvaging other sentinel ships (or get the fuel and resources for your sentinel ships)

Once you have acquire your first sentinel ship, things will become way easier. For starters, you will have a ship that is more effective at jumping between systems, requiring very few resources for refuelling. What's more, you can get a very cool looking ship with a unique launching animation. The process of ship hunting is like opening a lootbox, where even the trashiest outcomes (a C class ship that is not visually interesting), can yield almost 20 million credits when you scrap it. (you scrap ships in the space stations). Higher rarity ships can yield rewards up to 50 million credits.

After your first run, things can become more efficient. You can use your newly acquired wealth to buy massive amounts of resources required for starship batteries. Or, you can just use the 20 million credits to do other things. With that much money, you can easily complete the story mission, by buying everything you need. Capitalism is really efficient after all.

Here again lists the profits, assuming that massive amounts of harmonic mirrors are already acquired

Average ship yield (underestimation): 20 million per ship

Combat time: 5 minutes
System hopping time & time required to locate ship: 3 minutes
Harmonising the brain: 2 minutes
Scrapping the ship: 2 minutes

Total time: 12 minutes

Conservative yield: 100 million per hour

You can even sell your scraps in more profitable systems for additional profits

With relatively few setup, early to mid game players can very easily make massive amounts of profits. Hope this guide helps.