I think this has been nailed thx to ArcaneWeapon. What chiuyf says seems to be right as far as I can tell. I wrote a step by step guide that should help people with even a very basic intelligence find their seeds (Like myself). (Also deleted my question to stop it from confusing people.)
Before you start:
You need a Hex-Editor. (Personally, I use a NotePad++ plugin, but there may be better choices.)
A basic understanding of Hexadecimal helps but is not needed.
Step 1. Finding the 4 bytes that represent your seed.
Open your save game in your Hex-Editor of choice and search for the 5-byte sequence '93 e5 23 06 03'
In front of this sequence, there will be 4 bytes, so the whole 9-byte sequence becomes. '## ## ## ## 93 e5 23 06 03'. The first 4 bytes of the 9-byte sequence represents your seed.
Example: We use the search function to find '93 e5 23 06 03'. We add the 4 bytes before the sequence to get our 9-byte sequence. A 9-byte sequence from one of my games was 'd6 36 1a 34 93 e5 23 06 03'. That means that 'd6 36 1a 34' represents my seed.
Aditional Note: There is another method for finding the four bytes that represent your seed. If the save file is on turn 1, the 9-byte sequence will be located 197 bytes after "StandardMaps" in your savefile. If the save file is on any other turn you will instead find a sequence that goes something like 02 00 00 00 ## ## ## ## 03. In that case, you need to manually count down to the forth occurrence of 03, which will mark your 9-byte sequence where the first 4-bytes represents your seed.
Step 2. Converting the 4 bytes.
When you have your 4 bytes '11 22 33 44' you need to convert them. The seed is for some reason stored with the bytes in reverse. Therefore you need to reverse their order so
'12 21 34 43' becomes '43 34 21 12'
Example: 'd6 36 1a 34' represents my seed. I reverse them to '34 1a 36 d6'.
Step 3. Deciding if the seed is positive or negative.
Hexadecimal is simply another numeral system just like the normal decimal system we normally use, which means Hexadecimal can be converted to normal decimal. This has to be done to get your seed.
The conversion can be done quickly with either "
binaryhexconverter.com" or simply by putting Windows Calculator into Programmer mode.
When you convert you will get a normal number like '1212121212'.
If your number is lower than "2,147,483,647" this will be your game seed and you can jump to step 5 to get your map seed. If the number is higher than "2,147,483,647" your game seed was negative. This means we have to do another step.
Example for positive seed: I convert '341a36d6' on "binaryhexconverter.com". I get '874133206'. Since this is lower than '2,147,483,647' i now have my seed and I can jump to step 5.
Example for negative seed: I do the same as above but instead I get '2232819802'. This is higher than '2,147,483,647' which means my seed is negative and proceed to step 4.
Step 4. Converting a negative seed
To convert a negative seed we need to go back to step 2 and get our converted hex-number. '44 33 22 11'. Now we need to subtract this value from the hex-value 'FF FF FF FF'. The easiest way to do this is on Windows Calculator set to Programmer mode.
Do the calculation "FFFFFFFF-44332211". You will get a new hex value "BBCCDDEE". Convert this value to decimal (either via. the website or simply by pressing 'dec' under 'hex' in windows calculator. The decimal value is the seed.
Example: We got the value '2232819802' in step 3. The hex-value for '2232819802' is '8516205a'.
We do the calculation "FFFFFFFF-8516205a" and get the new value '7ae9dfa5'. We convert this value to decimal and get '2062147493'. We put this number in negative (*-1) and get '-2062147493'. This is our seed and we proceed to step 5.
Step 5. Game seed and Map seed.
Civ 6 uses two seeds. A game seed and a Map seed. If the seed we have found already is a positive seed it is our Game seed. If the seed we have found already is a negative seed it is our map seed.
To get our Map seed for the positive seed, we need to add +1 to our game seed. A game seed of '1212121212' has the corresponding Map seed '1212121213'.
To get our Game seed for the positive seed, we need to subtract -1 to our game seed. A neagtive map seed of '-1212121212' has the corresponding Game seed '-1212121213'.
Example:
We find the map seed for our positive seed: (874133206 + 1 = 874133206). We now have both seeds.
We find the game seed for our negative seed: (-2062147493-1 = -2062147494). We now have both seeds.
All credit goes to
OldManBrian
ArcaneWeapon
chiuyf
They were the smart people who actually figured all this stuff out.