zypper lr
abyss:~/Downloads # zypper install shells fish.repoAccording to your photo - you have - repository SUSE:SLE-15-SP1:GA is invalid
run -- and see if those repos are disabled and those repos are for the SLE (SUSE Linux Enterprise) not LeapCode:zypper lr
Direct link for 15.3 Fish Repository - https://download.opensuse.org/repositories/shells:fish/openSUSE_Leap_15.3/shells:fish.repo
Install the repository
Then try to install Fish
The next option is to upgrade to 15.4