It depends on the establishment. Some places will ask you to report legitimately, while some will let you work off the books illegally and not even record you as an employee. My last boss wanted realistic numbers, so I put in about 80% of my tips.
I guess I knew people in the 90's when everyone paid cash. I knew one bartender who had a stack of cheques she never got around to depositing because she was rolling in cash.
Yeah, the prevalence of credit cards make hiding all your tips, or even most of your tips, basically impossible now. Even if you did only declare your credit card tips, it's super suspicious to average 20% on cards and 0% on cash. Since your employer has to track tips, they usually want you to report something that's at least plausible.
When I delivered pizza as a side job back in the early 90s, I asked my manager how I should handle reporting tips and he said "Go ask James, he can tell you how it works." James was their senior driver, and a long-time friend from school, and he said, "I don't know about the other drivers, but I have never received any tips." I got the message. This was back before online ordering was a thing, and if somebody wanted to pay by credit card they would have to come into the store, so it was 99% cash. Every now and then a regular customer would pay by check, but the check would be made out to the company, so I would just take all my tips out in cash when I settled up at the end of the night.