Almost every backup system I've seen will keep multiple versions of the file around with decreasing frequency as time progresses, ie one for every day of last week, every sunday of the last month, the first of every month for the last year, etc. That way if you get hit by ransomware, you can restore to a point in time where you are (fairly) sure no infection was present yet. Nothing is perfect, but this does give a decent amount of protection for "most" important files as they tend not to change that often. For things that do change often like databases, different strategies may be needed.