try using EaseUS ToDo Backup - there's a free version at their web site that i've used for 6 years - Seagate's, Acronis, Samsung migration are all slow and won't let you in to add files to the backup disk
EaseUS, i clone the drive i want to save (no scheduled incremental backups as i'm afraid a virus/malware will get in or onto the backup drive before i know it's there), but as a clone, i can open any file on the backup drive and add or drop in files or changes to files just like any other drive - no hassle, no risk
try easeus one time and you won't waste your time with the others - plus Acronis screwed up on me twice ( backup was corrupted) and cost me a helluva work - i've had to use EaseUS backup copy 3-4 times, usually to overwrite...