I know that the end drug is smuggled in mostly from Mexico.
https://www.dea.gov/resources/facts-about-fentanyl#:~:text=Patients%20prescribed%20fentanyl%20should%20be,on%20the%20illegal%20drug%20market.
BUT, not on the backs of migrants-
Most of the fentanyl coming into the U.S. is trafficked
into the country through official land border crossings on the southwest border by transnational
criminal organizations. In fiscal year 2023, U.S. Customs and Border Protection (CBP) seized
240,000 pounds1 of drugs at the southwest land border, which included an estimated 1.1 billion
doses2 of fentanyl. Forty-four percent of total drug seizures and 99 percent of fentanyl seizures
occurred at the southwest land border.3 While transnational criminal organizations smuggle illicit
drugs into the U.S, they also illegally export currency from drug proceeds and firearms. This
illegal trade occurs at official ports of entry, alongside legitimate trade and transit, and CBP
personnel need more resources to enforce U.S. law.
The Stop Fentanyl at the Border Act would reduce the flow of fentanyl into the U.S. and crack
down on crime by providing much-needed funding, technology, and staffing increases at ports of
entry along the border. This bill would enable law enforcement officers to greatly expand
capacity for scanning vehicles and cargo to detect contraband before it enters the country, slash
access to supplies that dangerous drug cartels use to commit violence and crime, and prevent
illicit fentanyl and other drugs from entering the U.S. and harming American communities.
So, in other words- no Wall would stop it.  It is hidden in normal products being brought in legally.
Not so  much in the trunks of cars, etc, altho of course that happens. In shipping containers, trucks, etc.
From what I read, China makes the stuff or the precursors, ships to Mexico, then into USA.
Nor do they care about Border Security, except to trumpet OPEN BORDER, OPER BORDER OPEN BORDER- every chance they get.   It is just one of their three Big Lies-
The economy is horrible and it’s Bidens fault!
Crime is up, and it’s Bidens fault!
We have an open border and it’s Bidens fault!
All of which are lies.