*future me is like : wow this has become a long post*

I don’t like to be a “here’s a problem, you guys fix it or give me an answer” type of person and I’m actually interested in learning more about what’s going on.
The problem is that the car cranks but doesn’t run.

Here’s a sum-up of what I’ve tried. Not necessary in this exact position but close to it. It should give a rough idea of how things went and what I’ve tried.
The car engine turns around but doesn’t start and there’s no trying
I didn’t smell any fuel when trying to start
I’ve read out the car with my external OBD reader but no fault codes were showing
I have visible sparks at the plugs
The fuel pump doesn’t make a sound when I turn the ignition switch to position two and there’s no fuel pump sound when actually trying to start the car
I don’t feel or hear a click at the fuel pump relay
When I bypass the fuel pump relay on pins 30-87 in the fuse box, the pump runs
With a bypassed relay and audible running fuel pump, the car still doesn’t start
After approximately all of this fiddling (there’s a lot of googling and time involved) I found out that my external OBD reader isn’t able to read fault codes for this car *insert sad face here*
I decided to go to the garage where we always go and got brake cleaner. The mechanic said I could use that as a fuel replacement by spraying it in the intake but I shouldn’t use too much.
Since I’ve never done this before and “too much” is relative and vague to me, I may not have used enough.
The car didn’t start this way, maybe I was too careful, no idea.
After all of this(!) *insert another sad face here* I found that you can manually read fault codes.
You get in the car, press and hold the accelerator and the brake, put in the key, switch to position two and a light will start to blink representing fault codes.

I tried multiple times getting a code to blink but I got none.
I started double checking, this time a little quicker because I had knowledge.

The car didn’t start, but now I suddenly got fault codes:
Fuel pump relay not working
Fuel pump not working
Fuel level thingy not working

That could be correct ^ as they don’t seem to activate and between the two fault readings I’ve been working and disconnecting those things.
I’ve explained the problem to some people and they blamed the ECU of electrical failures, complete car broken, replace the ECU.

This above is like 7 months ago and up to now I didn’t create time to work further on it, also the battery was empty and I didn’t have a charger etc.

I came across “doit_vehicles” on YouTube 7 months ago but also again today.
This is the video from today: https://www.youtube.com/watch?v=pNwO8bI6-RY
He explains really well about the relays and fuses of the car, as well with an explanation to test them.
At 12:57 he mentions the ECU relay. I’ve been told by other people that the fuel pump relay (second purple in the video) is turned on or off by the first purple ECU relay.

However at ~14:03 in the video “doit_vehicles” pulls out the third yellow relay and says THAT relay controls whether to turn on/off the fuel pump relay.
If there’s someone I had to put my money on, it would be “doit_vehicles”

I cannot read electrical schemes so I can’t tell which relay actually is responsible for the (de)activation of the fuel pump relay.

I’d like to know what next steps I can take as I’m lost now.
For example, checking fuel pressure or the fuel filter seems unnecessary unless a filter can block the flow completely and a pressure sensor thinks there’s a leak due to low pressure which results in the car not starting. I could think of a hundred things like that.

The actual “funny” thing is we’ve had this car for three years and roughly 100k+ km or 62k+ miles. My GF was the main user of the car for her job. She buys a new car and this Opel switches over to me.
I start the car, drive forward and backward like 10 meters / 30 feet to make some room for the new car and a few days later I want to use it and it’s just dead.