The open_basedir is not been maintained, it still includes php73 directories. Nextcloud is secure enough IMHO, to disable open_basedir.
But of course, one could ad it as well but if this issue here already leads to a cry for help and the value has obviously not been maintained, I would recommend resetting the value, which is also the default.
So Adding /proc/cpuinfo alone is not enough, one have to adapt all the outdated pathes as well, which requires knowledge.