Hi Scott!
First, I want to thank you for your response. It helped me a lot!
But there are a couple of new problems I like to solve now. With your response I managed to create a folder with the name of the year. Also, I managed to rename the file the way I would like it, at least almost.
Here are my "new" problems:
1. The condition expression result always shots back with "false", even when the folder (e.g. 2021) exists

I took a quick look in the outputs from the "List folder" step and as you can see the folder 2021 exists and is listed in the output:
{
"Id": "%252fFreigegebene%2bDokumente%252fASC%252fAdministratives%252fLohnabrechnungen%252f2021",
"Name": "2021",
"DisplayName": "2021",
"Path": "/Freigegebene Dokumente/ASC/Administratives/Lohnabrechnungen/2021",
"LastModified": "0001-01-01T00:00:00",
"Size": 0,
"IsFolder": true
}
]
Here is a screenshot from the configuration of the condition step. I tried it with the "Name" and "DisplayName" variable from the "List folder" step. The output variable is the year.

2. The attachment file was named almost correctly

It would be nice if the step could name the file like this:
Example: 01_January_2021
The reason for the "0" is that teams listing or sorts files like this:
01, 02, 03 ...
and when you name your files like: 1, 2, 3 ... and when you come to "10" and above it will not sorted correctly. Here is a screenshot from what I mean:

Also I would like to add the month as text, shown in the example. Of course equal to the associated number of the month.
Thank you so much!
Greetings