This is likely caused by this bugfix "[SV 54740] Ensure .SILE"T settings do not leak into sub-makes” mentioned in the release notes https://lwn.net/Articles/810071/ which is bug https://savannah.gnu.org/bugs/?54740 on savannah. Turns out we would have wanted the buggy behaviour. Erik’s fix restores the behaviour that we want (ie propagation to sub-makes) though it might be better to add “--silent” at the beginning since MAKEFLAGS usually looks this:
s -j2 --jobserver-auth=3,4 -- FOO=bar
in a sub-make from a .SILENT make with -j2 and FOO=bar passed on the command line.