Sorry for the mess with paste in previous post.
The failing use case is the following:

~# update-alternatives --auto ebtables
update-alternatives: using /usr/sbin/ebtables-nft to provide
/usr/sbin/ebtables (ebtables) in auto mode
~# ebtables -N TEST
~# ebtables -P TEST DROP
Policy DROP not allowed for user defined chains.
~# ebtables -X TEST
~# update-alternatives --set ebtables /usr/sbin/ebtables-legacy
update-alternatives: using /usr/sbin/ebtables-legacy to provide
/usr/sbin/ebtables (ebtables) in manual mode
~# ebtables -N TEST
~# ebtables -P TEST DROP
~# ebtables -L TEST
Bridge table: filter

Bridge chain: TEST, entries: 0, policy: DROP

--
Regards,
Yevgeny