Middle mouse button paste does not work in all gtk applications

[jt]

Even though "Middle Click Paste" is enabled in gnome tweak tools, middle clicking does not paste. All GTK-applications that I tried are affected: nautilus, gmrun, the network widget. Even gmrun (older gtk application)

Middle click pasting does work in non-gtk programs.

I updated recently from ubuntu18 to ubuntu 20,
(Description: Ubuntu 20.04.2 LTS
Release: 20.04)

I do not use gnome as window manager.

ProblemType: Bug
DistroRelease: Ubuntu 20.04
Package: gnome-tweak-tool 3.34.0-2ubuntu1
ProcVersionSignature: Ubuntu 5.4.0-67.75-generic 5.4.94
Uname: Linux 5.4.0-67-generic x86_64
ApportVersion: 2.20.11-0ubuntu27.16
Architecture: amd64
CasperMD5CheckResult: skip
Date: Sat Mar 27 13:37:00 2021
InstallationDate: Installed on 2019-01-22 (795 days ago)
InstallationMedia: Ubuntu-Server 18.04.1 LTS "Bionic Beaver" - Release amd64 (20180725)
PackageArchitecture: all
SourcePackage: gnome-tweaks
UpgradeStatus: Upgraded to focal on 2021-03-20 (7 days ago)
modified.conffile..etc.bash_completion.d.apport_completion: [deleted]