My parents want to buy a new "family PC" and asked me to do a backup of their old iMac from 2013 running High Sierra. But my father doesn't want to use Timemachine because he believes that the data on the disk will become unretrievable without another iMac that runs the same OS once they'll switch to Windows in a year or so. Now this doesn't sound right to me, but since I haven't used Apple products in a very long time, I have no way of knowing if this is true or not given their disdain for obsolete products.
My parents want this HDD just as a safety backup in case something happens to the new PC so long-term compatibility with both OS is their top priority.
Should I just format the disk as exFAT and use Timemachine without thinking about it too much, or should I just manually copy every single folder just to be safe?
Thanks in advance for your help.