What about the myriad of apps that I sometimes need to make things work like claws-mail that doesn’t exist for leap 15.6 or darktable that is much much too old for 15.6 or emacs that is really, really old on leap…
If you use the onboard search tools you will find that claws-mail is available in the standard OSS repo for Leap 15.6:
test@leaptest:~> sudo zypper info claws-mail
Refreshing service 'openSUSE'.
Loading repository data...
Reading installed packages...
Information for package claws-mail:
-----------------------------------
Repository : repo-oss (15.6)
Name : claws-mail
Version : 4.2.0-bp156.1.2
Arch : x86_64
Vendor : openSUSE
Installed Size : 11.5 MiB
Installed : No
Status : not installed
Source package : claws-mail-4.2.0-bp156.1.2.src
Upstream URL : https://www.claws-mail.org/
Summary : A configurable email client
Description :
Claws Mail (previously known as Sylpheed-Claws) is a
configurable email client and news reader based on the GTK+ GUI
toolkit, and it runs on the X Window System.
When claws-mail is executed for the first time, a configuration "wizard"
(dialog) will appear prompting you for the minimum information necessary to
create a new account.
test@leaptest:~>
Instead of using OPI which installs packages from developement repos, you can always use the built in tools like Discover (Plasma) or Gnome Software (Gnome) and install apps via Flatpak.