What's the "Address"?
Queen’s Speech | The Institute for Government
It is rare for the government to be defeated on the address in the Commons – as governments usually have a majority in the House. But it has happened – most recently in 1924, when Stanley Baldwin’s minority government was defeated. Baldwin then resigned as prime minister, and the opposition went on to form a new government.
https://www.ka.edu.pl/download/gfx/ksw/pl/defaultaktualnosci/1162/23/1/electionam.pdf, 5.
Stated simply, these conventions are, first, that the incumbent Prime Minister has the first opportunity to continue in office and form an administration; secondly, that if he is unable to do so (and resigns, or is defeated on the Address or in a no confidence motion at the meeting of the new Parliament) then the Leader of the Opposition is appointed Prime Minister; and thirdly, it is for the political parties to negotiate any inter-party agreement for government among themselves without royal involvement.
Colin Faragher's Public Law Concentrate 2019, 15.
In the event of a hung Parliament the incumbent Prime Minister has the first opportunity to continue in office and form an administration. If he or she is unable to do so (and resigns, or is defeated on the Address or in a no confidence motion at the meeting of the new Parliament) then the Leader of the Opposition is appointed Prime Minister. It is for the political parties to negotiate any inter-party agreement for government among themselves without royal involvement.