I know that some American tourists actually do this, on giving servers cash tips as if they’re underpaid by their employer (since they’re used to it in the USA along with growing up with that mindset) but overlook the fact that servers are paid the minimum wage in the EU, as it’s not “typically” the norm. This practice is being exported it seems, in another region where that isn’t common.
As long as workers in the respective country are paid and are not entirely dependend on tips: no.
I also don’t get paid extra money just for doing my job that I am already being paid for. It is so weird and asymmetric that tips are a thing in gastronomy and hospitality. As if these were the only low-wage jobs that can sometimes suck a lot.
If someone is unhappy about their wage, they need to take it up with their boss or organize in a union. It is not my responsibility to pay them.