Quality issue exporting Aerial footage from DJI Mavic Pro

Hello Community,

I'm desperately seeking an answer as to why all of the drone footage I ever edit looks poorly compressed after exporting from FCPX. I recieved from a drone operator HEVC .h265 4k footage from the DJI Mavic pro 2 drone, and it looks good.

Step 1. I trans coded the footage by exporting a 4k from QuickTime, then trans coding in Mpeg stream clip (I know I'm still using this old software, I'm old and not sure what else to use, it still works well, I try handbrake but it screws up any motion and it looks pixelated when creating an mpeg4, I'm open to suggestions).

Step 2. Then brought the footage into FCPX, color corrected edited, added my titles and graphics and exported a .H264 file and, it now looks like crap and looks slightly compressed, slightly, but enough to notice and not understand why it always looks like crap after exporting from FCPX.

I'm not sure what to do I've been trying to figure this out for years, I rarely work with aerial footage which is why I'm back on trying to figure this out and need some help. I'm delivering this to a client asap.

Any help on this would be SO VERY MUCH appreciated! Thank you!