I don't use itsme, only CSAM, because itsme does not support Linux: I can't log in with Firefox or Chrome on Linux with my eID. But CSAM is not universally supported. Example of a site that does not support it: https://www.proximus.be/ - Major ISP in Belgium)
https://www.brusselstimes.com/belgium/246070/federal-governm...
The Belgian government already has an implementation: https://www.csam.be/en/egov-profile.html
I don't use itsme, only CSAM, because itsme does not support Linux: I can't log in with Firefox or Chrome on Linux with my eID. But CSAM is not universally supported. Example of a site that does not support it: https://www.proximus.be/ - Major ISP in Belgium)