Here's the Maps of where the settlements are found.

Sometimes you just don't care about legitimately unlocking settlements.
Luckily, there's an easy way to unlock all settlements anytime and anywhere you want.
I originally planned to make this a script, but unfortunately this was not possible.

Open the console by pressing ~ (US Layout)

Other layouts use different keys.
Here's a list of keys that may work, based on language layouts:
Taken from fallout.fandom.com

• Belgian: ù (point keyboard)
  
• Brazilian: `
  
• Canadian Multilingual Standard: è
  
• Danish: Æ
  
• Estonian: ü
  
• French: ² or ù
  
• Finnish: Ö
  
• German: ^ or ö
  
• Hungarian: ö
  
• Icelandic: Æ
  
• Italian: \ or | or ò
  
• Japanese: @ (to the right of P key)
  
• Norwegian: ø
  
• Portuguese: ç
  
• Russian: ё
  
• Spanish: ñ
  
• Swedish: å or ö
  
• Swiss: ¨ (The upper key of the left of the enter key)
  
• Turkish: "
  
• United States: ~ or ` (to the left of the number 1 key)
  
• United Kingdom: ' (below the @ symbol, on the same key)
  
• Other possible solutions: §, ½

In the console, paste one of these lines and hit enter. Then copy and paste the next and so on.
Closing the console should get you a "You can now use the workshop at XXX" message.
Swapping the 1 for a 0 at the end of the code will remove the ability to use the workshop
Replace the xx in the ID with whatever prefix your DLC has. The number is based on load order.
If Far harbor is first on the list, swap the XX with 01, or just 1.

Should you not know the Prefix of your DLC, search for anything contained in the DLC.
For Far Harbor, use "Help tektus 0". You should be able to see NPC_ "High Confessor Tektus"
In the picture below, you can deduce that all Far Harbor settler ID's also start with 03

For Nuka World you can look for N.I.R.A. using "help nira 0"

For Vault 88 stuff, look for "88"
For Automatron, look for "Mechanist"

Note:
The Mechanist Lair will not actually be unlocked and accessable until the last quest is finished.
Luckily you can jumpstart that quest by using the command "setstage xx0010f5 400"
Unfortunately though, you can not just jump through the stages using SetStage to finish it, because that breaks the mechanist lair.

Commands to spawn usable settlers are:

Warning:
Settlers spawned through this command will not be assigned to any settlement.
You must manually move them to the settlement you want them to be in.

Some Settlers can not be commanded, moved, or used in caravans.
For example:
Sturges can be commanded to do stuff, but you can't move him to another settlement.
The kids at the Warwick Homestead don't have any options at all.

To turn literally any NPC into a regular Settler, use the following commands on them:
If the NPC is hostile, add them to your player faction by using the following command:

I happened to stumble into cricket at the Warwick Homestead and decided to "keep her".
Now she's a settler of mine and also sells me stuff.


If the "select NPC by mouse click" thing does not work, use prid to target them instead.
Because, sometimes the mouse ends up selecting an effect, or a particle, or whatever instead.

You can also teleport any NPC to you by using
And then turning them into a settler.

All these values are "Actor Values"
Actor Values can be handled with the following commands:
GetAV VALUE_ID to find out current value
ModAV VALUE_ID # to modify value by #. Can be negative to lower the value
SetAV VALUE_ID # to set value to exactly #

Example:
ModAV 32e 40 adds 40 available power to the settlement.
ModAV 330 -5 removes 5 required power from any appliance you picked.


Needs:

Other

Here's some other Stuff that is not related to settlements specifically, but may be useful.

Copy-paste the following command into the console to instantly get perk points.
Replace the # with the amount of points you want. Does not affect level

This adds all Piket Fences magazines near you on the ground.
Pick them up to unlock building special objects.
You can save this as a txt file in your FO4 install location called "Mag.txt"
Then ingame use "bat mag" to run this code and have all mags spawn next to you quickly for any future playthroughs.