F29: dnf upgrade does nothing

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link text <availability> specifies whether advisories about newer versions of installed packages (omitted or --available), advisories about equal and older versions of installed packages (--installed), advisories about newer versions of those installed packages for which a newer version is available (--updates) or advisories about any versions of installed packages (--all) are taken into account.

I'm using it for getting list of available security udates.

dnf upgrade

run successfully after 3 calls of it.

You're confusing list of advisories with list of available package updates. I tried to say it in my answer, but maybe wasn't clear enough. Advisory is some statement or posting (i.e. a text message) about found/fixed vulnerabilities or bugs. For example look at sudo dnf updateinfo --all info FEDORA-2019-f31c14682f. This advisory reads: "This update addresses various overflow conditions that could result in possible memory read/write out of bounds errors or zero byte allocations when connected to a malicious server." It also lists vulnerabilities fixed (for libssh2). That's the advisory.

Moreover, that's the advisory for package that was already updated.

Use sudo dnf check-update form the list of updates that you can actually apply right now.

Use sudo dnf check-update --refresh to force dnf to update it's database (i.e. to get new list of updates available).