Here an update:
by default, MS Access sets linked tables with "unlimited" NUMERIC
to DECIMAL with "precision: 28" and "decimals: 6" (MS Access names).
Trying to read a value [INSERT INTO public.demo VALUES (1.0 / 3)]
breaks with an error.
When creating the column using NUMERIC(28, 24), MS Access shows this:
"precision: 28" and "decimals: 24". And there's no error.
Funny, when creating the column using NUMERIC(32, 28), MS Access
interprets it as TEXT with field length 32.
NUMERIC(28,27) is the last column type, MS Access can read as DECIMAL.
A view on an "unlimited" NUMERIC with casting ::NUMERIC(28, 24)
is accepted by Access. So it seems like I need to create a VIEW as a
work-around.