Where can I practice the language exam for citizenship?

Start here.
https://www.leforem.be/particuliers/formations-langues.html

Pre Covid booking an exam test was fast. You also have to do a one on one oral test. The test is done on a computer and questions get harder or easier to find your level. Quite clever.
For citizenship the level is not difficult.

contact www.bon.be They are government agency and it can be done for free and it is officially recognized.