Relying on a job, the income ceiling in first-tier cities should be around 20k RMB after tax, with only a few industries reaching 30k RMB after tax.

Exceeding 20,000 to 30k RMB after tax is basically impossible; those who can break this limit are not ordinary people.
If you're not in a first-tier city, then this ceiling should be multiplied by a factor of 0.5 to 0.7.
There is a deliberately designed bottleneck in employment, intentionally making it difficult for the vast majority of people to pass.
This is similar to the acceptance rate of Tsinghua and Peking University—everyone works very hard, and the number of applicants varies each year.
But the acceptance rate for Tsinghua and Peking University is always around 0.7%, and it will never change; it’s always a very tight cutoff.
Some people might disagree and say, "I know someone who earns 50k or 60k RMB a month working a job."
Actually, it all depends on the duration.
If you can maintain this high income for more than five years, you are truly exceptional—a rare talent among many.
This is the reality of working a job.
If you want higher income, you need to consider other methods.