pinyin input not working in many apps, e.g. firefox, remmina ...

I'm using Ubuntu's Chinese (Intelligent Pinyin) IME to write Chinese. This worked mostly flawlessly until I upgraded from 21.04 to 22.04.

Since then, Pinyin input won't work in the following applications:

- Firefox (snap)
- VSCodium
- Remmina
- Keepass XC
- MS Teams

Notably, Pinyin input _does_ work in many other apps, e.g.

- Most apps that ship with GNOME (e.g. Terminal, Settings, launcher, ...)
- Zim
- LibreOffice

ProblemType: Bug
DistroRelease: Ubuntu 22.04
Package: ibus-pinyin (not installed)
ProcVersionSignature: Ubuntu 5.15.0-39.42-generic 5.15.35
Uname: Linux 5.15.0-39-generic x86_64
ApportVersion: 2.20.11-0ubuntu82.1
Architecture: amd64
CasperMD5CheckResult: unknown
CurrentDesktop: ubuntu:GNOME
Date: Mon Jun 20 18:03:51 2022
InstallationDate: Installed on 2020-04-01 (810 days ago)
InstallationMedia: Ubuntu 19.10 "Eoan Ermine" - Release amd64 (20191017)
SourcePackage: ibus-pinyin
UpgradeStatus: Upgraded to jammy on 2022-04-05 (76 days ago)