This notion of 'opening the border' is a political myth conservatives have been using to justify their increasingly extreme positions for years, much like their inflammatory use of the word 'invasion'.
The border was de facto open since there was no serious enforcement. Because there was no space to detain millions of people, the majority were processed and then simply let go into the U.S. with a "Notice to Appear" set for 2030. Basically a free pass to stay for years.
On top of that, they had parole loopholes (like the CBP One app and CHNV) to legally admit millions more people.
