Store matching files in iCloud AND on Mac and Macbook I signed up for iCloud storage for added security (in case my local computers crash or are stolen), but am finding out iCloud is trying to only keep certain frequently used files also on my Mac (running 10.13.6) and Macbook Pro (running 11.1).
If I lose internet, power goes out, or iCloud gets hacked and everything gets deleted/corrupted, I think the cloud-only documents are vulnerable to loss. My goal is to always have safe and complete versions of the files and no “dehydrated links / stub files for download on demand data on my computers.

assume both Macs have more free storage than my iCloud storage quota
Assume both are online and internet is fast enough for syncs to happen regularly and efficiently

Is there a way to force iCloud to keep all files at all times current in both my local machines?
First and foremost: iCloud is not a backup service. In order to achieve what you want, you need backups!
You can use various forms of backups to realize your goal: For example you could use the built-in Time Machine software with external USB-drives in order to have a complete backup that you could store at a seperate location. You could also use a cloud service such as Backblaze, SpiderOak or similar.
That being said, you can avoid the Mac removing files from your local disk to free up space by opening up System Preferences, click Apple ID and then remove the check mark from Optimise Mac Storage.