There are several things you can do to steepen your learning curve. This thread is not about "how bad is Fusion" or "I like something different" so my recommendation is based solely on using Fusion 360. I use Fusion almost exclusively and found there are no limitations in it for what I need to accomplish. I use the "Personal" (free) version and after having used the "full" version, I found that there are workarounds to every limit placed on the free version. For example, export the files (.f3d/.stl/whatever) to your computer and the "10 limit" isn't a factor. Here are a couple of tips for Fusion:
1) Watch a lot of YouTube videos (as most have said). Have Fusion open and follow along while the video is playing the "second" time. In other words, watch the video, then watch it again while doing it on Fusion. I like Tyler Beck videos.
https://www.youtube.com/@TylerBeckofTECHESPRESSO
2) Focus on parameters and constraints. Once you master those, parametric design is simple and those makes a world of difference and can lower the frustration level. Also, to a lesser extent, learn the "Project" command early!
3) Reverse-engineer a part or object. Have it in hand so when you "design" it in F360, you have something you can directly relate to. This helps you visualize the part a lot easier in F360. You can take dimensions straight off the part and when done, and if you print it, you'll have a something to compare it to and see where things worked and didn't work.
4) Start by using Tinkercad to design a simple part. Then design the same part in Fusion. This will allow you to see the relationship between commands and outcome. Tinkercad is about as simple as it gets for CAD so relating the simple functions between the two helps. They are both Autodesk products (Autodesk didn't start TC, they bought them).
5) Start all designs in 2D sketch/Solid. Once you master the program, you can move to Surface modeling where it's a little more difficult to size the object initially.
No matter which product you use, it will all boil down to familiarity and experience.
The infils are generally done with your slicer. It can be done in a CAD program but in most cases, it's probably better to let the slicer optimize the infill. Dissolvable supports are controlled in the slicer with specific material settings. Not really any different than other FFM printing material.