Thanks to EOS, I am looking forward to install Arch Linux on my personal daily drivers as well as on my office machine.
On each machine there is Debian Stable running so far, which never had any trouble after updates.
The interesting question now is:
The Arch Linux whitepapers also claim it to be a rock solid system - is this true in reality or do I have to tinker around updates sometimes? 
think the question differs from person to person : what is stability?
general here it runs stable , mayby got issues but its not so much.
in time in arch things change and need manual intervention but thats not a part of a stable because things change and need to move a bit. does not means its unstable, its just keeping a eye of arch news. sometimes we find also things out and will notify everyone.
a newer kernel can always have some bugs offcourse its always wisely to have a linux-lts beside the linux kernel. each first point release of a new kernel version can be edge. but does not mean arch is more unstable on other distroās.
its mather of personal experience also i think
A rock solid system in its core, so it is indeed a rock solid system core, this excludes stuff running on top of it like X-system.
So the system itself will boot 99% and the 1% left will be easy to solve.
But sometimes you need to fix stuff running on top of the base system, like apps you are using the DE or X-Server stuff like gpu driver and connected framework.
The āGUIā stability (what you do need to get your business work done mostly) depends also hugely on what you do with your system. If you are tinkering on every little aspect of your DE theming, performance try programs refining everything e.t.c.e.t.c this will brake your system much more often. If you take what you get, do not use AUR stuff that much system DE and X will be stable as a rock and if something brake solution will be fast and easy (mostly someone will post the solution here in short time)
Thank you for your answers! 
Haha, no I wonāt not at all. 
I am just asking about basic office software like LibreOffice, Thunderbird, Dolphin & Co., because I would be a little bit annoyed if this stuff fails every week due to unstable updates.
Ask this to @FredBezies I think he is using an Arch since 2009, I will let him to confirm itā¦if this is not a sign of stability, what it is ?
Keep Rollingā¦ 
me since 2007 
my wife using EndeavourOS for office-work and watching streams and before Antergos with only one brake of x-system over 5 yearsā¦
I lost! 
2007 ! I bow downā¦there is no more proof to bring here about stability on rolling Arch 
ā¦perhaps mention of frequency (recommended) and volume of updated packages could be suggested to one used to Debianās update particulars
I have been using Debian Unstable and EOS in parallel on my home machine for some time. I donāt see any difference in stability. Both have their pros and cons.
Uh, a comparison between Debian Unstable and EOS is not very advantageous for EOS. Better to compare Debian Stable with EOS.
My personal experience is that I have far better experiences with rolling distro over leaping in general and with Arch over other rolling distros specifically. Even Manjaro is way more unstable than Arch for me (counting EndeavorOS as Arch here due to using Arch repos and more importantly the Arch kernel).
I also want to point out that rolling distros are not Unstable. The distinction should be Leaping or Rolling, not Leaping and Unstable.
By leaping you mean being able to migrate to the next major version right?
Whether with terminal operations (like Debian) or with GUI mostly automatically (like Ubuntu)
Manual interventions (see history of https://www.archlinux.org/news/) must be mentioned.
Which is why Arch and EndeavourOS arenāt for the general public.
Which is the different from Solus or Manjaro[1] who target the general public IIUC.
[1] which I hope will get mature enough compared to my last experience few years ago. I had way less maintenance on my Cinnarch (which became Antergos, which I migrated to EndeavourOS )
Or maybe compare EndeavourOS with Debian testing? I think Debian testing has also manual interventions from time to time, right?
But the package stability policy of Debian testing seems less strict (due to itās role) that the one of Arch Linux. The comparison isnāt still relevant enough IMHO.
(Debian users opinions welcome to correct me if iām wrong)
Yes exactly.
As for manual intervention: this is true, but if you run an Arch based distro you should be able to copy detailed instructions from the Arch homepage. The most difficult part of Arch is install and config. If you get EndeavorOS, Archman, Arco or Manjaro installed and configured to your liking you should be able to handle that. Not to mention if you install pure Arch.
Personally I use a RSS reader in Firefox that checks the Arch news channel.
Debian testing is per definition NOT stable while Arch is
Before it was URSS !!! 