Hello J.,
After reading this Q&A /7911 on this same subject: https://forum.plantuml.net/7911/how-do-you-add-a-link-to-multiline-component.
1/ If there is only one link at the end of the description, you can put directly ']]]' at the end of the description and do:
@startuml
rectangle rectangle [[http://www.google.com]] [
====
Title: rectangle
....
Reference1: [[https://www.google.com]]]
@enduml
[Click to see on PlantUML online server]
2/ If there are more links, you can use this workarond, adding '\n\' after the link on the description if there are at the end of some lines inside the description:
@startuml
rectangle rectangle [[http://www.google.com]] [
====
Title: rectangle
....
Reference1: [[https://www.google.com]]\n\
Reference2: [[https://www.google.com]]]
@enduml
[Click to see...]
If that can help,
Regards,
Th.