Comment # 1 on bug 1173706 from Felix Niederwanger

I'm having the same problem on a fresh Leap 15.2 install. The problem occurred
already in Tumbleweed in https://bugzilla.opensuse.org/show_bug.cgi?id=1172316
and got fixed there (according to the bug report).

phoenix@mjoelnir:~$ flatpak --version
Flatpak 1.6.3
phoenix@mjoelnir:~$ flatpak search Blargh
error: While opening repository /var/lib/flatpak/repo: opendir(objects): No
such file or directory
phoenix@mjoelnir:~$ flatpak remote-add --if-not-exists flathub
https://flathub.org/repo/flathub.flatpakrepo
error: While opening repository /var/lib/flatpak/repo: opendir(objects): No
such file or directory
phoenix@mjoelnir:~$ ls /var/lib/flatpak/repo
phoenix@mjoelnir:~$ 

I can also confirm that the suggested workaround (delete /var/lib/flatpak/repo)
works:

phoenix@mjoelnir:~$ sudo rmdir /var/lib/flatpak/repo
[sudo] password for phoenix: 
phoenix@mjoelnir:~$ flatpak remote-add --if-not-exists flathub
https://flathub.org/repo/flathub.flatpakrepo
phoenix@mjoelnir:/var/lib/flatpak/repo$ flatpak search steam
Name         Description                                                       
        Application ID                                   Version  Branch
Remotes
Steam        Manage and play games distributed by Steam                        
        com.valvesoftware.Steam                          1.0.0.64 stable
flathub

On Tumbleweed the Flatpak version is 1.6.4, on Leap 1.6.3