Yum/Dnf で下記のエラーが発生します。

# yum install wget
Rocky Linux 8 - AppStream              0.0  B/s |   0  B     00:03
Errors during downloading metadata for repository 'appstream':
  - Curl error (60): Peer certificate cannot be authenticated with given CA certificates for https://mirrors.rockylinux.org/mirrorlist?arch=x86_64&repo=AppStream-8 [SSL certificate problem: certificate is not yet valid]
Error: Failed to download metadata for repo 'appstream': Cannot prepare internal mirrorlist: Curl error (60): Peer certificate cannot be authenticated with given CA certificates for https://mirrors.rockylinux.org/mirrorlist?arch=x86_64&repo=AppStream-8 [SSL certificate problem: certificate is not yet valid]

時刻がずれている可能性があります。chronyc で時刻を同期させましょう。

# chronyc makestep

あまりないと思いますが、ルート証明書が古い場合はルート証明書を更新します。

# yum install ca-certificates

どうしても解決できない場合はリポジトリの設定 (/etc/yum.repos.d/*.repo) に sslverify=0 をつけます。

[appstream]
name=Rocky Linux $releasever - AppStream
mirrorlist=https://mirrors.rockylinux.org/mirrorlist?arch=$basearch&repo=AppStream-$releasever
#baseurl=http://dl.rockylinux.org/$contentdir/$releasever/AppStream/$basearch/os/
gpgcheck=1
enabled=1
countme=1
gpgkey=file:///etc/pki/rpm-gpg/RPM-GPG-KEY-rockyofficial
sslverify=0