I have not tried running Freesurfer version 5 on CentOS8, but it would not surprise me if it is not entirely compatible with the newer versions of the system libraries on CentOS8.

The Freesurfer version 7 beta release just came out this February (MailScanner has detected a possible fraud attempt from "surfer.nmr.mgh..harvard.edu" claiming to be https://surfer.nmr.mgh.harvard.edu/fswiki/dev7beta1) and development is working on getting the full release out (with subsequent 7.X point releases to follow).  So I think the expectation going forward is for users to eventually migrate from freesurfer 6 to 7.  But I don’t know of any planned updates or changes to rev 5 (which is essentially 2 releases old now).

If you want to maintain OS compatibility for older freesurfer releases, then one option is to use a VM or a container to keep and run older versions of CentOS.   I think CentOS6 is going to be end of life'd this coming November, but you should be able to download virtual disk images of the last release of CentOS 7, 6, 5, etc. for quite some time from osboxes.org and other sites.

- R.