UTM - OpenVPN Client - AES-GCM

Getting GCM to work in SSLVPN would mean to upgrade the openvpn version, which means to upgrade and test all sub components of this module. It is not a pure apt-get upgrade - it is more likely a huge effort to do this. 

SFOS already supports this ciphers and other further upgrade. So maybe a upgrade to SFOS would resolve your need, especially if you are a home user. 

I am not a home user.
We have OpenVPN in use on many clients.
Instead of migrating to SFOS, I'm more likely to switch to another enterprise product. 
The excuse of a huge effort does not apply in security products.
It has been known since at least 2019 that the CBC Ciphers is considered vulnerable.

CBC is vulnerable? You mean this? https://success.qualys.com/discussions/s/question/0D52L00005lbJrVSAU/why-are-cbc-ciphers-considered-weak

I think it is very poor that sophos does not present GCM on openvpn but on ipsec they do. GCM is used almost everywhere instead of cbc. We have vpn routers same age or even older as sophos utm wihich offer GCM and ctr. They are supposed to be faster and more safe as cbc. We think about changing our openssl system.

I think it is very poor that sophos does not present GCM on openvpn but on ipsec they do. GCM is used almost everywhere instead of cbc. We have vpn routers same age or even older as sophos utm wihich offer GCM and ctr. They are supposed to be faster and more safe as cbc. We think about changing our openssl system.