Except that itsme crap is not from the government and doesn't support activation on anything but a Windows / Mac machine. No Linux support at all, while the Belgian government stuff (CSAM) supports Linux just fine.
It is from the banks that leveraged their KYC but was adopted very broadly by gov and many other id required or linked services. AFAIK it does not need a computer to activate besides your phone and one of those bank issued 2FA challange card readers.
For CSAM, also AFAIK, first 'activation' includes a visit to your local municipality to verify your identity. Unless you go via itsme, as it is and authorized CSAM key holder.
Unless your bank supports it, you will need a windows/mac computer to activate, as it uses the https://plugin.connective.eu/ browser plugin to read out your ID, which doesn't support Linux. Maybe it has changed, last I tried was more than a year ago and that time, my bank (AXA) couldn't be used to activate, so the only other option was browser activation.
For CSAM, also AFAIK, first 'activation' includes a visit to your local municipality to verify your identity. Unless you go via itsme, as it is and authorized CSAM key holder.