The Cartographers' Guild has a discord server that can probably be found with a quick Google. It's not active all the time but fairly steady occasional activity.

A lot of people there use photoshop or hand-draw but Campaign Cartographer isn't uncommon to come up either.

Here is my attempt at similar not too long ago:

I mention in a later comment the sheet effects I used. I mostly just remember it took a lot of fiddling with a lot of effects to arrive at the result.

Spent 45 minutes messing around with the marine dungeon and got this so far. Under the rocks on the left-side is the entrance to the dungeon. Lots to tweaks to make yet but let me know what you'd want to see.

I love the city so far! I especially liked how purposeful each placement of building is. One thing that looks a bit odd to me is the straightness of that bottom left line, almost as if the city planner was tired of doing all this and just cut off the boundary of the city sharply. ;)

Just for my own knowledge, historically, I'm curious if building walls out in the water was a thing? I had the assumption that sea-walls would be built directly on the coast, and then since harbors tended to be at sheltered locations, places would float massively heavy chains with barrels between the most outer points of the coastline. (see https://en.wikipedia.org/wiki/Boom_(navigational_barrier) ) - but I would love examples where walls were built.

Whether historically accurate or not, I think it's pretty cool. I would make up reasons for the walls to be there if I had to in order to include them.

I don't know my history as well as I should but I just kind of imagine an arthurian age where most people of power are corrupt and everybody knows it but is too fearful to stand up to it, so they purposely keep that fear cycle turning with public displays of punishment. Getting in good with certain officials means you are untouchable, up to the point of your usefulness anyway, so crime is common and it is a risk to even try and prevent it from happening.

Then the players enter.