YOU (Yast Online Update)
YOU (Yast Online Update) only addresses security updates from the official repositories. Does that mean YOU (Yast Online Update) is not to have my system new/est but fix the security issues have been found?

It means that the Leap system, which does keep to the same versions of software throughout it’s lifetime, is up-to date (with security and recommended updates).

But when you have other repositories, like Packman, YOU does nothing with them. So you must handle those separately. I start e.g. YaST > Software > Software Management, the choose the Repositories from the View menu, the click Packman at left and at right do a Right-Click, which shows a context menu where I click “Update if a newer version is available”, then Continue.

Others do a zypper up.

Is there a software in official repositories can’t fix the security issues unless updating to the latest version?

I see you are on 15.4 and it looks to me you are questioning if it is time to move to 15.5.

For that see Lifetime - openSUSE Wiki

So 15.4 is supported until end of this year.

So what are you missing if you do not run these patches. Hard to say, your personal PC is I think not interesting to an hacker so likely the risk is low.

The thing is that to make a decent guess on how secure something is not so simple.

Sorry, but there seems to be a language gap, because I do not understand what you try to say.

But again, when you do YOU (or similar zypper) you get the security and recommended patches. That includes security patches that are upstream published for newer versions of their software, but those are then back-ported to the LEAP version you use. Thus you will not be more secure when switching to that newer version, because you will have the same security patch.

Thank you.

Sorry, it is caused by uninstalling software not by full-upgrade

openSUSE Leap 15.4 is expected to be maintained until end of November 2023, not end of this year (December).