The term "app" has been used for 30 years for applications that run on PCs, mainframes, or micros. The use of "apps" for iPads/tablets is 30 years later, and does not mean for tablets. Those that deny history will repeat it.
In answer to a number of combined questions - Final Cut Pro X, Resolve, and Premiere are all full featured aps capable of yielding professional deliverables, and run on PCs. The tradeoff with their capability is complexity. Starting off with easier to use solutions can be a good choice, if you don't have any plans to take your edits very deep. Cut editing, simple transitions, and limited color correction is certainly possible in them. If you think you may need to get more sophisticated in the future, recognize that you will need to go through 2 learning curves, the first for the simple app, and then again for the more complex. For the most part, the learning on the first app is thrown away, as the more complex app has it's own interface, and way of doing things.
With older computers, and many new ones, the DJI codec used in 4K imagery is best processed by transcoding the footage to some codec more edit friendly - on the Mac ProRes is the best choice. Ifs you don't transcode before inputting, both Resolve and FCPX allow you to make edit friendly proxies which are very edit friendly, and produce output from the full quality original for delivery.
Streaming media such as YouTube and Vimeo will transcode your output to a streaming format they have optimized for streaming. It is adequate, but if you have been looking at the footage on a 4K calibrated display, you will see significant image quality loss. Vimeo gives you more control of this, and provides higher quality streaming results.