They are mainly offering VDSL2 connections over phone lines. They also offer Fiber over a monopolist's (called Proximus) GPON infrastructure, but the rollout of that GPON network is still in early stages. However, that monopolist has pledged to accelerate that rollout in light of the increasing work-from-home statistics following the pandemic.

https://www.proximus.com/news/2020/20201208-proximus-brings-...