Does Oracle 11gR2 is supported on RHEL 8 or Oracle Linux 8? Oracle (afaik) did not updated their compatibility matrix yet. Can I run Oracle 11gR2 (which still is in extended suporte) in the new OS?
Most likely you can run it without any issues but it is not supported by Oracle. As Phil suggests in his comment this combination will never be supported as you are mixing an almost out of support database (extended is over on December 2020) with a just added Linux release.

Best solution is use Oracle 12.2 which, in my experience, is a minimal problem migration target for most applications using Oracle 11.  The 12.2 release allows an easy upgrade to Oracle 18 or 19 when the time comes.