Write your files list into file_list.txt
file_list.txt
file /mnt/d/Videos/video_part1.mp4 file /mnt/d/Videos/video_part2.mp4 file /mnt/d/Videos/video_part3.mp4
Call following command in bash.
ffmpeg -safe 0 -f concat -i file_list.txt -c copy video_merged.mp4