It’s not necessary that your computer can’t handle 4K playback it may just be it can’t handle 4K in the codec or compression ratio that comes straight from the drone.
Consumer computers are optimized to playback more compressed video files that you would get as like a downloaded movie or something. Videos that have already been edited are outputted as highly compressed files where the movie studio or video distributor has done most of the computing for you up front so your computer doesn’t need to do it.
Now people that edit videos want the least possible compression from the camera because they will edit it and then compress it themselves later when they distribute it. This allows for higher quality video output. So the files coming from the drone are in a less compressed state for this reason. The compression amount of the video can be measured by the bit rate of the video and the resolution. By lowering the bit rate of the video but not the resolution you can maintain the resolution and visual quality while making the size of the video smaller and easier for your computer to play.
If you do not edit your video or you do edit but your computer can’t handle it all you need to do is re-encode the video at lower bit rate. By doing this you will make it easier for your video to play without reducing the video quality in any noticeable way.
There is a free and open source program called Handbrake which offers industry leading video encoding.
HandBrake: Open Source Video Transcoder
It can also be used to convert higher resolution video to a lower resolution but you may not need to do that.
Just choose one of the preset options and let it go to town. Depending on your computer‘s power this could take a large amount of time but you can cue up several videos and let it run over night.