GCM ist newer, faster and more reliable than CBC.
More and more companies are switching to GCM.
Also with OpenVPN 2.4 GCM is preffered by server-default.
If you take a look at the .ovpn files, there is an "ignore server default" command
ncp-disable
followed by the personal choosen cipher (for example)
cipher aes-256-cbc
If this option "ncp-disable" is removed, the 256-GCM is always used, independent from the configurated or choosen chipher (overriding)...because it is the preffered default chipher.
You should choose the 256 or 128-GCM profiles at the Download area