Hello A.,
- Would that be enough?
@startuml
title Bracketed line thickness
node foo
foo --> bar : ∅
foo -[thickness=1]-> bar1 : [1]
foo -[thickness=2]-> bar2 : [2]
foo -[thickness=4]-> bar3 : [4]
foo -[thickness=8]-> bar4 : [8]
foo -[thickness=16]-> bar5 : [16]
@enduml
See also: https://plantuml.com/en/deployment-diagram#b5f6831632fd63c1
If that can help,
Regards,
Th.