Generally Datasources are published at a project level, meaning that only the workbooks in that specific project will be able to see the Datasources
There is a small "workaround" that I've found online here: How to publish one data source to be utilised across many projects in Tableau Server – datatoffee
Hopefully it points you in the right direction.
Thanks , managed to figure it out with the help of your workaround link
Glad it helped - could you mark my reply as the correct answer if you're happy with the result.