BUDAPEST — Hungarian lawmakers are preparing to vote on a constitutional amendment viewed by many critics as both a crackdown on the freedoms of assembly and expression and the most recent move by the populist government to restrict the rights of LGBTQ+ communities.

The amendment, which will almost certainly be passed Monday by the two-thirds majority of Prime Minister Viktor Orbán’s nationalist Fidesz party, would permanently codify a ban on public events held by LGBTQ+ communities —…