Hi, @Andree Holz! Welcome to the community!
You can't use the same key between accounts. You must create new keys for each individual Bitbucket account.
In this case, I would suggest you add this SSH key on this Jenkins user (not as an access key to the repository) and give them read access to the repositories you need. This way, you can use this SSH key on multiple workspaces/repositories.
In case you would like to read more about SSH keys, you can access the following link:
I hope this helps, but please let me know if you face any obstacles.
Kind regards,
Caroline
