1.792-vsc1.33.1I cannot see how to install an extension from a .vsix, the files seem greyed out.

.vsix to /tmpchmod 777 <filename>.vsix.vsixIf you do the equivalent of this in your Dockerfile they install properly. This is what we've been doing and it seems to work pretty well.
RUN mkdir -p /home/coder/.code-server/extensions
RUN curl -JL https://github.com/mhutchie/vscode-git-graph/releases/download/v1.4.5/git-graph-1.4.5.vsix | bsdtar -xvf - extension
RUN mv extension /home/coder/.code-server/extensions/git-graph-1.4.5
Thanks! That worked for me. Still an issue that you can't install from a .vsix though.
I have the same issue, on the latest version.