On-screen keyboard does not allow to input any accentuated char
It's a known issue that the GNOME on-screen keyboard, on X11, does not allow input of chars that are not supported by the current keyboard layout: for example, long-press on the "a" button will show you "à", but pressing the "à" button won't input a "à" letter in an English session. OTOH, in Tails 3.15, in a French session, this would work just fine. But on 4.0~beta2, even in a French session, pressing the "à" button does not input anything at all. This is a regression.
Upstream (GNOME) issue: https://gitlab.gnome.org/GNOME/gnome-shell/issues/109
This was supposedly fixed by https://gitlab.gnome.org/GNOME/mutter/commit/e3e933c47a69bd137bb83b3692d105d1261d16ff, which was released in mutter 3.32.2. Buster has 3.30.2 (and so does Sid, currently).