Why not? You probably run an armv7 based install (and removal was announced half a year ago!)? 
Please avoid posting screenshots only and non-english contet 
Also have a read on how to ask a good question 
Sorry for the german screenshot and thanks for your answer. To give a little more details:
i am running HA OS on Proxmox on a ASUS NUC 13 Pro (Intel Core i3-1315U)
“uname -m” on the Proxmox Node gives me “x86_64”.
Here is also a screenshot with “ha info”
My system architecture is amd64. This means you i should not have been affected by the removal of armv7 support of ESPHome, right?
Maybe someone had similar issues?
Just as an FYI,
my qemux86-64 still sees it in the Add-on Store and can install it.
However, not sure what your problem might be.
[Edit] Update, just came across the following:
There is a supervisor bug at the moment that makes HA not detect installed addons correctly.
A possible fix is being tested in the developer channel and should soon be released if no issues with it are found.
There are quite a few posts about the issue with the MQTT addon.