There is no baseline file in this version, so the equivalent is a hand-maintained list of patterns — and the maintenance is the part that decides whether it stays useful.
$ vendor/bin/phpstan analyse --no-progress 2>&1 | grep 'was not matched'
Ignored error pattern #Access to an undefined property# in path
src/Legacy/* was not matched in reported errors.
# a pattern matching nothing is a line to delete.
# running through them quarterly takes twenty minutes.The unmatched-pattern report is on by default and easy to miss in a long output, and it is the whole maintenance mechanism. Without it the list only grows, and a list that only grows is a way of appearing to have adopted the tool. Patterns should be as narrow as the error allows — a broad one silences errors that would now be worth seeing, in code that has since been rewritten.