The earthquake that struck Turkey and Syria has killed over 11,000 people and devastated the infrastructure of the region.
According to Syrian activist Abdulkafi Alhamdo there are four border crossing between Turkey and Syria, “But they [the convoys] are only carrying dead bodies of Syrian [quake] victims in Turkey back to Syria.” Even the Syrian Civil Defence, also known as the White Helmets say that no aid is reaching Syria.
The Biden Administration categorically denies that our sanctions have anything to do with the lack of humanitarian supplies going to Syria.

“Any US or international sanctions include humanitarian, medical, food, and other aid exemptions. US President Joe Biden was clear when he said the US was prepared to provide any and all types of aid to the people of Syria, and the US is not preventing any countries from doing so,” a State Department official said in Arabic.
“The United States stands by the Syrian people,” the official said in a video posted to Twitter.

Only two months ago UN Special Envoy for Syria Geir Pedersen said the U.S. sanctions on Syria "shouldn't block humanitarian assistance."
It's clear and obvious how are sanctions are blocking humanitarian aid to Syria.

Local sources told Al Mayadeen that numerous international shipping firms have refused to land in Syria out of fear of US and EU sanctions after several countries have asked Syrian airline companies to transport tonnes of aid aboard their civilian airliners, which are not properly equipped for transporting such large amounts of aid.
...Social media users have been sharing a screenshot from live flight trackers showing how Turkey's airspace is full of air traffic while neighboring Syria to the south does not have any air traffic whatsoever, signaling how the whole world was quick to send aid to Turkey in stark contrast with the situation in Syria.
Some sources have revealed that so far, some 62 aid teams from 50 countries have made it into Turkey while barely any have made it to Syria

Even the Lebanese Hezbollah have manged to get humanitarian aid to Syria, yet the U.S. and UK haven't managed it.