So I want to know if it is possible, that a bot gets the content sent to it in a dm and send that in a specifyed channel on a server.
So basically you dm the bot the word "test" and the bots sends the word in a channel of a server
Yes, it is possible for a bot to receive a direct message and then repost the message in a specified channel on a server. This can be done using the Discord API.
You can do the following:

Create a Discord bot and add it to your server. You can do this using the Discord developer portal.

Use the Discord API to listen for messages sent to the bot in a DM. You can do this using the message event and the DMChannel class in the Discord API.

When the bot receives a DM, use the Discord API to repost the message in the specified channel on the server. You can do this using the send method of the TextChannel class in the Discord API.
Getting content from a dm in discord.py