I am getting following error .

yum.repos.d]# yum repolist enabled
Loaded plugins: langpacks, product-id, search-disabled-repos, subscription-
: manager
This system is not registered with an entitlement server. You can use subscription-manager to register.
file:///opt/Mariadb/MariaDB-server-10.3.20-1.el8.x86_64.rpm/repodata/repomd.xml: [Errno 14] curl#37 - "Couldn't open file /opt/Mariadb/MariaDB-server-10.3.20-1.el8.x86_64.rpm/repodata/repomd.xml"
Trying other mirror.
file:///opt/Mariadb/MariaDB-server-10.3.20-1.el8.x86_64.rpm/repodata/repomd.xml: [Errno 14] curl#37 - "Couldn't open file /opt/Mariadb/MariaDB-server-10.3.20-1.el8.x86_64.rpm/repodata/repomd.xml"
Trying other mirror.
repo id repo name status
mariadb MariaDB Repository 0
repolist: 0

under /opt, I have copied rpms manually and created mariadb repo under /etc/yum.repos.d/.

Repo as

db.repo.old media.repo redhat.repo

cat mariadb.repo

[mariadb]
name=MariaDB Repository
baseurl=file:///opt/Mariadb/MariaDB-server-10.3.20-1.el8.x86_64.rpm
gpgcheck=1
enabled=1

yum.conf file as

etc]# cat yum.conf
[main]
cachedir=/var/cache/yum/$basearch/$releasever
keepcache=0
debuglevel=2
logfile=/var/log/yum.log
exactarch=1
obsoletes=1
gpgcheck=1
plugins=1
installonly_limit=3

cat /etc/redrel

Red Hat Enterprise Linux Server release 7.5 (Maipo)