No i386 package libgtk3-nocsd0

[Lubensius]

While starting an 32bit application on an 64bit System (Ubuntu Mate 20.10LTS, Multiarch) ther is an error message "ERROR: ld.so: object 'libgtk3-nocsd.so.0' from LD_PRELOAD cannot be preloaded" which is correct as in /usr/lib/i386-linux-gnu/ there is no libgtk3-nocsd.so.0.
If I try to install it with

sudo apt-get install libgtk3-nocsd0:i386
...
E: Paket libgtk3-nocsd0:i386 kann nicht gefunden werden.

https://packages.ubuntu.com/focal/libgtk3-nocsd0 shows no i386

ProblemType: Bug
DistroRelease: Ubuntu 20.04
Package: libgtk3-nocsd0 3-1ubuntu1
ProcVersionSignature: Ubuntu 5.4.0-48.52-generic 5.4.60
Uname: Linux 5.4.0-48-generic x86_64
ApportVersion: 2.20.11-0ubuntu27.9
Architecture: amd64
CasperMD5CheckResult: skip
Date: Sun Sep 27 15:29:05 2020
InstallationDate: Installed on 2018-01-01 (1000 days ago)
InstallationMedia: Ubuntu 16.04.3 LTS "Xenial Xerus" - Release amd64 (20170801)
ProcEnviron:
 SHELL=/bin/bash
 LANG=de_DE.UTF-8
 TERM=xterm-256color
 XDG_RUNTIME_DIR=<set>
 PATH=(custom, user)
SourcePackage: gtk3-nocsd
UpgradeStatus: Upgraded to focal on 2020-07-18 (70 days ago)

[Launchpad Janitor (janitor)]

Status changed to 'Confirmed' because the bug affects multiple users.