I newly (since a few weeks) found this bug and reported it, see Embeds and images not shown when filename contains umlaut (ä, ü, ö).
Funnily enought, I only started with using snap to rule out influence of non-supported installation methods for reporting another bug…
Sooooo, I should just drop the snap and use which of the installation formats and from which source? Or are there other workarounds?