few days ago I published this #HowTo
https://xosem.gitlab.io/trim-ssd/
checking now if the weekly timer was working as expected... it was not! :blobthinkingcool:
#ArchWiki didn't give any (further) clue about whats going on wrong. The two crypted partitions were not trimmed. The non-crypted was.
:blobfacepalm: :blobfacepalm: :blobfacepalm: :blobfacepalm: :blobfacepalm:
... I'd forgotten intall and write GRUB config after passing the discard to LVM config. Kill me truck!