How do I get back the older way of (not) displaying dead key presses?

Question

Some characters in my language (Czech) are typed using 'dead keys' (key presses that don't move the caret) followed by a letter receiving the diacritics prepared in the previous dead key stroke.

The old way was that nothing was displayed at the dead key press only. After upgrading from Linux Mint 19.3 (x64, Cinnamon) to 21 (the same arch and window manager), the dead key press displays a diacritics symbol to be added to the following letter.

How do I get the old way of not displaying anything until the final letter?

setxkbmap -print -verbose 10
Setting verbose level to 10
locale is C
Trying to load rules file ./rules/evdev...
Trying to load rules file /usr/share/X11/xkb/rules/evdev...
Success.
Applied rules from evdev:
rules:      evdev
model:      pc105
layout:     cz
options:    grp:win_space_toggle,terminate:ctrl_alt_bksp,grp_led:scroll
Trying to build keymap using the following components:
keycodes:   evdev+aliases(qwertz)
types:      complete
compat:     complete+ledscroll(group_lock)
symbols:    pc+cz+inet(evdev)+group(win_space_toggle)+terminate(ctrl_alt_bksp)
geometry:   pc(pc105)
xkb_keymap {
    xkb_keycodes  { include "evdev+aliases(qwertz)" };
    xkb_types     { include "complete"  };
    xkb_compat    { include "complete+ledscroll(group_lock)"    };
    xkb_symbols   { include "pc+cz+inet(evdev)+group(win_space_toggle)+terminate(ctrl_alt_bksp)"    };
    xkb_geometry  { include "pc(pc105)" };
};

UPDATE 1: It affects GTK applications (like xed text editor, Gnome terminal, Chrome, LibreOffice) while Qt applications like notepadqq work the old (desired) way.

set -x XMODIFIERS @im=none did not help

UPDATE 2: Installing ibus (Intelligent Input Bus - core) package introduces the problem also to Qt applications.

Answer 1

This was most probably a bug, which disappeared after the last update:

less /var/log/apt/history.log

Upgrade: libxapp1:amd64 (2.2.14+vanessa, 2.2.15+vanessa), xapps-common:amd64 (2.2.14+vanessa, 2.2.15+vanessa), warpinator:amd64 (1.2.13+vanessa, 1cinnamon:amd64.2.14+vanessa), libmuffin0:amd64 (5.4.6+vanessa, 5.4.7+vanessa), bulky:amd64 (2.4, 2.5), muffin-common:amd64 (5.4.6+vanessa, 5.4.7+vanessa), cinnamon:amd64 (5.4.11+vanessa, 5.4.12+vanessa), webapp-manager:amd64 (1.2.4, 1.2.5), cinnamon-control-center-data:amd64 (5.4.6+vanessa, 5.4.7+vanessa), gir1.2-meta-muffin-0.0:amd64 (5.4.6+vanessa, 5.4.7+vanessa), libcinnamon-control-center1:amd64 (5.4.6+vanessa, 5.4.7+vanessa), cinnamon-common:amd64 (5.4.11+vanessa, 5.4.12+vanessa), mintreport:amd64 (1.3.4, 1.3.5), gir1.2-xapp-1.0:amd64 (2.2.14+vanessa, 2.2.15+vanessa), cinnamon-control-center:amd64 (5.4.6+vanessa, 5.4.7+vanessa)

I suspect cinnamon:amd64 was the cause of the problem.

Wrong. I must have set it and the setting applied after logging out/in. It doesn't have anything to do with the update.
After installing Mint 21 to a new computer, the problem was back and no updating helped.

Correct answer:
Start minlocale-im (e.g. using Alt-F2).
Set input method framework to XIM (the select is on the top of the window).
Logout/login (or restart your computer).