This is a sample project that defines a couple optional typeclass instances using No More Orphans trick. More details are in the accompanying blog post.
Use SBT to run the test suite:
git clone https://github.com/7mind/no-more-orphans.git
cd no-more-orphans
sbt test
Tested on Scala 2.12.12, 2.13.3, 2.11.12 (2.11 only works partially) and dotty
Addendum: the pattern may not work for non-higher-kinded types on Scala 2 (i.e. plain types like Int, not type constructors like List[_] or typeclasses like Monad[_[_]]).