Will immigration reduce the wages of local people? What does this have to do with supply and demand?

Generally speaking, immigrants will lower their wages. But it's not that simple. On the one hand, immigration will increase the population of a country, and the competition for a job will also increase. Just as the increase of college students in China leads to the overall decline of the salary level of fresh graduates. On the other hand, the increase of population may also lead to the increase of national GDP and the increase of profits created for enterprises, thus leading to the increase of national average income. In which direction, we have to consider the quality of immigrants. For example, Canada has a small population, so it encourages immigration, but encourages immigration through normal channels, because normal immigrants are screened and of high quality, which is easy to benefit the country. But it will also put an end to smuggling, because although it can also increase the population, the quality of immigrants will be reduced, and these people will seize the job opportunities of low-wage nationals and will not create much social value. From the perspective of supply and demand, Canada wants immigrants to fill the employment gap, because the population is in short supply. China, on the other hand, discourages immigration because China is overpopulated and millions of college students can't find jobs. What do you need so many people for?