Almost, @Tristan_VILLERS. That’s up to repository maintainers to fix, not package maintainers. I have the same (and unfortunate constant issue) with StoneSoup developers’ repo. Debian dropped SHA1 in favour of SHA256 early last year and some repos are taking their sweet time to follow suit.
Debian maintains (used to maintain?) a list of repos that haven’t done the transition yet, but I can’t find it now. Nonetheless they get contacted periodically by Debian to do so.
Just an update to this – I noticed their key had expired/changed some weeks ago, and since using their new key, this error doesn’t appear anymore (it’s the same remote URL, so Boutique didn’t need updating).
Considering this one fixed.
(An easy way is to just re-install it from the Boutique, this’ll import the new key)