I've heard that when a new president is in office they usually sign a document that says they pledge not to discuss Israel's nuclear weapons. According to the New Yorker:

The first iteration of the secret letter was drafted during the
Clinton Administration, as part of an agreement for Israel’s
participation in the 1998 Wye River negotiations with the
Palestinians. In the letter, according to former officials, President
Bill Clinton assured the Jewish state that no future American
arms-control initiative would “detract” from Israel’s “deterrent”
capabilities, an oblique but clear reference to its nuclear arsenal.
Later, Israeli officials inserted language to make clear to Washington
that Israel would “defend itself, by itself,” and that it would,
therefore, not consider the American nuclear arsenal to be a
substitute for Israeli nuclear arms. George W. Bush, when he became
President, followed Clinton’s lead, signing a similar letter, former
officials told me.

Desmond Tutu also wrote a comment piece in the Guardian urging Biden to “end the US pretence over Israel’s ‘secret’ nuclear weapons”.

Has President Biden refused to sign a letter or a document keeping the number of Israel's nuclear weapons secret?