Actually I just looked into this for my wife. $6800 is the max before you having to call CRA/CCP about it. $19K is the cutoff where they deem you may not need CPP. You call them in between those numbers and they can review if full CPP is still required or if adjustments should be made. Don't get me wrong the CPP amount plus $19K is still a low income...but you may be able to earn a bit more if capable.
https://www.canada.ca/en/services/benefits/publicpensions/cpp/cpp-disability-benefit.html
expand the sunstantial gainful work section
The other replies spell some of it out, but there are some things I should note so you have a broader picture.
Some provinces have pharmacare so after a max deductable (based on income) your medicines are free. If you are disabled you can also apply for a provincial form that makes all medicines free (no max starting deductable)
If you have a provincial disability designation you can get dental, eyeware, drugs, therapy, devices needed covered by a special provincial health insurance. The person you asked may not have been aware of this, or they live in a province that has a higher threshokd of what constitutes disability. (The reason I say unaware is their statement about $6800 max earnings is not correct) The only downside is you don't have a list of what is covered, you have to submit the cost or try for preapproval. Why it is a secret about what is covered is a mystery...I can only assume to stop people reading through and taking advantage of free stuff??
If you have cancer and out of work their is a cancer fund that supplements your income. However they look at previous years earnings to determine eligibility, so if you were healthy then suddenly got sick, rather than slow decline in earnings, you have no funding available because of high amount on last tax return. You would have to wait till the following year when you file a low income tax return to get help.