Problem phenomenon

$ sudo dnf update
EPOL
Errors during downloading metadata for repository 'EPOL':
    -Status code: 404 for htpp://repo.openeuler.org/openEuler-21.09/EPOL/repomd.xml (IP: 159.138.**.***)
Error: Failed to download metadata for repo 'EPOL': Cannot download repodata/repomd.xml: All mirrors were tried

solve

Method 1.
the official has pushed the update. The updated file is located in
/etc/yum.repos.d/openeuler.repo.rpmnew ,
it needs to be manually compared and updated to the original
/etc/yum.repos.d/openeuler.repo
for the differences between the two files, see baseurl Path Method 2 in method 2 below.
directly manually modify the baseurl address of epol
baseurl= http://repo.openeuler.org/openEuler-21.09/EPOL/ $basearch/
is modified to
baseurl= http://repo.openeuler.org/openEuler-21.09/EPOL/main/ $basearch/