How can I transfer my destiny 2 character from the PC to the xbox series s?

Steam, bungie, pc

There's no such thing as a "transfer" per se. However, you can enable Cross Save. However, you should follow the instructions in this regard, especially with regard to any DLCs you may have purchased:

https://www.bungie.net/7/de/CrossSave

In what way? So not with the DLC but with the character? Will the weapons be taken along?

You keep characters and existing weapons - it will simply be available everywhere, as long as you activate the current account for Cross Save.

Thank you

So as I thought

Then another quick question: Could I now transfer my Steam PC account to my PS4 and later also to the Xbox? So that I can play the same characters on multiple consoles.

Yes…