In a high level, you are correct that Ubuntu is a standalone OS like Fedora. Other distributions have used the background packages that make up Ubuntu to form their own OS with changes here and there. It is similar to how Ubuntu is built on top of Debian.
Sure others can explain this better.
Since you are more familiar with Windows, Linux Mint may be a good start. Can also try PopOS for a different desktop layout, more similar to Mac. These are Ubuntu based systems. Can also give Fedora a try, but may require a bit more of a learning curve. There is also Nobora for a more gaming oriented version of fedora. Try out the live previews before installing to make sure your system works properly.
Not sure if this is something that will help but the site Linux Journey might help you learn how to use and understand Linux more. This is more the core stuff and command line oriented.
For easier transition, start using programs that are available on both systems so you don’t have to jump in cold turkey, if that may be too much. When looking for programs on Linux, always use the provided store first to search. Since you are a programmer, you are aware that there will always be multiple ways to do the same thing, web searching is your friend, just make sure you are searching for the right based system, in the examples above, Fedora or Ubuntu. For programming you are going to enjoy Linux more than windows :).
Remember this is a journey and will take time. Have fun!
On Neo store, f-droid front end, in the settings there is an option to auto update all apps. Also has a one click button to update all apps if you don’t want to auto update.