@PatsJolla, @naokysatoh et al:
Finally managed to get Storeman installed by using the 4.5 release
I was struggling to find a correct storeman rpm.
Please do mind:
See also Feedback on Jolla C2 - #605 by olf
P.S.: Storeman Installer v2.2.8 had a bug which prevented it from installing Storeman, Storeman Installer v2.2.6 and v2.2.7 were always working fine for all SailfishOS releases (i.e. including 4.6.0 and 5.0.0).
Unfortunately (but as usual), it took weeks until someone filed a proper bug report, then it was fixed within two days by releasing Storeman Installer v2.3.0.
Kudos to @norayr and @HenriVSL (maybe @henuka or @hene) for their valuable support.