There are very different rules. Like worlds different.

Comparing just Belgium and the Netherlands right next to each other. The Netherlands is quite doable if you find a job. Some automatic work visas and then residence based on that depending on origin country

In Belgium literally no company in the country outside of IMEC and Deloitte will go through the extremely long visa sponsorship program (only digitalized in 2022 IIRC). It is pretty much only possible if you have family or a partner that already lives there. Even people studying there for 3-8 years have a few months to find a job or they are kicked out (in a bad job market compared to other countries also).