strace actually helped me get further: searching for more info about “keyboxd”, I came across this:
Commenting out “use-keyboxd” from ~/.gnupg/common.conf make it work again for me. Interestingly, I don’t remember creating this file myself, and I don’t seem to have my keys there anymore. Perhaps some package had my ~/.gnupg overridden? In any case, it’s all working now.