The advice of using HANDBRAKE to convert the 4K H265 to different encoding is a plus! Many households these days have a 4K television capable of playing your favorite memories. If you wish, you may certainly upload to YT @ the 1080 rate. But, I might also suggest many persons dabbling in videography/photography these days are going at a little behind the times. What I refer to is the home laptop/desk computer. To obtain optimal results in post production, I would recommend having a system capable of doing so. Many systems can easily be updated by simply adding RAM, some need replacement. Many machines come standard with only 8 MB RAM. Most video production recommend a minimum of 16-32. Also, make sure your monitor is able to view at higher resolutions as well. More RAM reduces possible video drag.
Numerous post production programs are available, but the top 2 I recommend are either Adobe Premiere Elements 2029 or 2121 and DaVinci Resolve 16 (stable). Adobe will cost about $100 (but usually you can find package deal of the PE with the Photoshop Elements for $100, and NO CLOUD REQUIRED), Resolve is free with higher learning curve (usually for more experienced).