How do I efficiently backup locally without a cloud or a second Unix-like system on the network?
If you do not go for a second system, your backups stay online and onsite, so there is a very high probability for them to get destroyed at the same time as your original.
By refusing to go to a cloud, you then need to host yourself that second system that will backup your data.
By refusing to go for a second Unix-like system, you drop to a last option : a second system that will run Windows.
That system will be higher risk than your original in many ways. Windows filesystem is terrible, the operating system is designed to crash, security holes are the daily news and more.
Should you use your Windows system as a gateway to offline storage like DVDs, you end up with a very limited capacity for storing your data. A DVD holds less than 5 G of data...
So you are asking for something that will magically transfer, store and restore a high volume fo data without any effort. That will not happen auto-magically.
So as
@danb35 suggested, define your backup needs first :
what data ?
how big ?
how often do they change ?
how long a history do you need ?
do you want to protect yourself against physical threats ?
do you want protection against logical threats ?
what is the acceptable gap between two backups ?
Once you defined your needs, it will be possible to design a solution.