I have no evidence that there are fewer illegals in the country now than four years ago. However, the premise is that there are twelve million MORE illegal immigrants now than previously.
Until someone can produce anything that suggests this is true, the argument that rents are higher because of 12 million NEW illegal immigrants is false. After all, there were as many illegal immigrants in 2010 as there are today. There is nothing, then, to suggest this is Biden's fault.
You don't need definitive numbers to support your claim. Just something published that gives a reasonable estimate.