It may be a lot better if you say which backup software you have tried, and why the ones that did not meet expectations fail the test.
also, a quick google for "backup software free" shows:
Best free backup software - at a glance:
EaseUS Todo Backup Free.
Cobian Backup.
Paragon Backup & Recovery.
FBackup.
Google Backup and Sync.
https://www.pcworld.com/article/3235812/the-best-free-backup-software-and-services.html has some reviews of some of these at the bottom. It might pay to read them and at least get more familiar with backing up, backup options, pro's and con's etc.
If you have never used backup software before, then it may be that the idea you have for backing up is flawed. no fault of yours, but sometimes in I.T. the questiion you asked is not really the right one.
for example, some of the ways your current idea is flawed:
- your working files and your backups are in the same place. A lightning strike, fire, dog/cat accident at the PC, fire sprinkler damage, theft could all result in both working and backups going bye-bye.
- A ransomeware would likely encrypt working and backup files
- a problem with working files will likely get copied to your backups.
All that aside, a search for software/tutorials using the keyword "incremental" is what will steer you right.
lastly, consider online backup. once the initial big backup is done, subsequent ones are not that big, and it is totally off-premises, safer and the backup companies think of things you dont!
PS. a windows forum may be a better place to ask.