I’m about to check this. Also and related to our next day conversation:
My upload test (.jpg file is on this forum converted to .jpeg extension, as visible when opened within new Tab) was successful (I’ve made another post with upload today as well). Perhaps you might want to Save as related file to .jpeg right away. Perhaps log out from this Forum => log in helps there.
EDIT: If you are indeed out of working space (and you never wanted to accept this as a fact), and if I’m guessing right (as I do not know for sure) and as you already introduced yourself to @marcf post, df -kh / and expansion of / partition related, are you out of /home directory space there?
Furthermore, @Sharon, upload might therefore not work from Librem 5 (if available partition space is at its minimum) and by copy of this screenshot to some external USB drive (or external SD card device over USB-C port) you’ll be able to upload it (or attach it to the related E-mail) from another computer.