minimize and maximize missing on window bar

When logging in via RDP (xdrp) the buttons minimize and maximize are missing at the top of each window (left of the destroy cross which is available at the top-right).

The window color scheme also is light-grey, not the default Ubuntu 20.04 dark-grey.

The destroy button does not show in a red circle when the window has focus.

ProblemType: Bug
DistroRelease: Ubuntu 20.04
Package: xrdp 0.9.12-1
ProcVersionSignature: Ubuntu 5.4.0-88.99-generic 5.4.140
Uname: Linux 5.4.0-88-generic x86_64
ApportVersion: 2.20.11-0ubuntu27.20
Architecture: amd64
CasperMD5CheckResult: skip
CurrentDesktop: GNOME
Date: Sun Oct 17 10:56:34 2021
InstallationDate: Installed on 2020-04-06 (558 days ago)
InstallationMedia: Ubuntu 18.04.4 LTS "Bionic Beaver" - Release amd64 (20200203.1)
SourcePackage: xrdp
UpgradeStatus: Upgraded to focal on 2020-04-17 (547 days ago)