Also what video editor have you used to merge the whole video? I know there're plenty of softwares, but a great number of them destroy the quality so much...
What? Which ones? Most (at least half way decent, and yes, also the Plenty of free ones) ones are able to export in high quality or even Uncompressed (which of course will result in an Huge File usualy, depending on length of whatever you export. Make sure your PC can play those back, if you try to use uncompressed formats, as they can be pretty demanding in terms of Hardware needed for Smooth playback) Quality. If your Editing software outputs bad quality files, check your Settings for Export (or whatever the specific Software calls those). Usually increasing Bitrate by quite a bit should help with quality, if you are using compressed Formats like .mp4 or anything else H.264/ H.265 / Quicktime /ect.
If that still isnt High enough Quality, try to change export File Format/ Codec to an Uncompressed/ Less Compressed Format/ Codec.
In terms of Bitrate for .mp4 Files with H.264 Compression, 8000 kBit/s should be Plenty for FullHD Resolution, even i use less sometims if i need smaller files, like to upload them here.
If you have a ton of random Noise or glitter or something like that (a lot of fast and randomly changing color and Brightness Information in the Images compared to the Following frame/-s), you might need WAY more than 8000kBits to make it look reasonably good. The Less changes within your frame, the lower Bitrate will usually be enough to result in an Similarly good looking final image in the exported File.