As @phoog linked, you should always try to follow official information from government website and have a refugee travel document issued by the U.S. before trying to enter Canada.
But as a side note, the message on the government website is probably the result of a confusion. If you have some really urgent need to visit Canada, you can still attempt crossing at a land border.
The April 26 regulatory changes only concerned the ETA requirement, not the passport exemption for U.S. LPRs requesting admission direct from U.S. at a land border (IRPR 52(2)(b)). A valid passport or travel document is always required for air travel due to a separate regulation. For whatever reason, IRCC decided to put a much broader change on the website.
Even in May 2022, the CBSA/IRCC operational guide says
13.16 Passport and travel document exceptions
[...] Permanent residents of the U.S. seeking to enter Canada from the United States or
St. Pierre and Miquelon. Note that U.S. Permanent Resident Cards are only
acceptable upon presentation on contiguous territory and not valid for international
flights from outside Canada unless accompanied by a valid and subsisting passport
or travel document;