Healthcare in Belgium, how does it work?

Hello,
After many years as "digital nomad" I'm now retiring. I left my native Denmark in the eighties, and at this time I no longer feel at home here. I enjoyed my time in Brussels for many reasons, including the central location and milder climate, so have chosen to retire there.

Since Denmark and Belgium are both EU countries, moving there is relatively easy with the "free movement" laws, but I struggle to understand the healthcare system in Belgium.  In Denmark we have what I believe is called "universal healthcare", i.e.  most healthcare treatment is "free". Not as in free beer but as in you're not directly charged for treatment.  That goes both for doctors visits and hospitalizations. Prescription medications are partly reimbursed following a complicated system.  All covered through general taxation.

In Belgium it is my understanding that you have to pay partly to the government, and partly to a private insurance, but how much and how.  I have read both https://www.socialsecurity.be/ and https://www.dkv.be/ but I'm probably a bit slow mentally as it is still very vague to me how it works.

Things like:
- Where to register for healthcare
- how much does it cost, is there maybe a price list?
- what does it cover?
- What happens when someone has a preexisting conditions that the private company will not cover?