At level 20, Druids get access to the following feature:
At 20th level, you can use your Wild Shape an unlimited number of times.
Additionally, you can ignore the verbal and somatic components of your druid spells, as well as any material components that lack a cost and aren’t consumed by a spell. You gain this benefit in both your normal shape and your beast shape from Wild Shape
The emphasis is on the fact that you can ignore verbal, somatic and non-consumed material components, which makes these spells imperceptible, as per Xanathar:
If the need for a spell’s components has been removed by a special ability, such as the sorcerer’s Subtle Spell feature or the Innate Spellcasting trait possessed by many creatures, the casting of the spell is imperceptible.
Counterspell requires you to be able to see a creature casting:
Casting Time: 1 reaction, which you take when you see a creature within 60 feet of you casting a spell.
As a result, it seems to me that it is impossible to ever counterspell a level 20 druid unless they use a material component that is consumed.
Am I missing something? Is the level 20 Druid feature essentially 'become immune to counterspell' as a hidden bonus? Or is there still a way to counterspell them?