Slow X11 performance through ssh

[Vasilis]

Running remote X11 applications (more pronounced on those built on top of python-tk or tcl/tk) connected through ssh -CXY in the recent 24.04 resulted in extremely slow performance, which makes it almost impossible to work.
My computer that is affected, was based on xubuntu 20.04LTS and upgraded constantly up to 24.04LTS

For testing, I prepared USB sticks and boot on them (Try ubuntu) so as to have a clean system

Look the following screen recording

https://youtu.be/KYZn3rbFduI

The first time I am trying with lubuntu 24.04LTS USB stick
The second time with xubuntu 20.04LTS USB stick

the difference in performance is visible.

ProblemType: Bug
DistroRelease: Ubuntu 24.04
Package: xorg 1:7.7+23ubuntu3
ProcVersionSignature: Ubuntu 6.8.0-41.41-generic 6.8.12
Uname: Linux 6.8.0-41-generic x86_64
ApportVersion: 2.28.1-0ubuntu3.1
Architecture: amd64
BootLog: Error: [Errno 13] Permission denied: '/var/log/boot.log'
CasperMD5CheckResult: unknown
CompositorRunning: None
CurrentDesktop: i3
Date: Thu Aug 22 11:19:27 2024
DistUpgraded: 2024-06-03 14:19:47,372 DEBUG migrateToDeb822Sources()
DistroCodename: noble
DistroVariant: ubuntu
DkmsStatus:
 virtualbox/7.0.16, 6.8.0-39-generic, x86_64: installed
 virtualbox/7.0.16, 6.8.0-41-generic, x86_64: installed
ExtraDebuggingInterest: Yes, if not too technical
GraphicsCard:
 NVIDIA Corporation TU104GL [Quadro RTX 4000] [10de:1eb1] (rev a1) (prog-if 00 [VGA controller])
   Subsystem: NVIDIA Corporation TU104GL [Quadro RTX 4000] [10de:12a0]
InstallationDate: Installed on 2021-12-02 (994 days ago)
InstallationMedia: Xubuntu 20.04.3 LTS "Focal Fossa" - Release amd64 (20210819.1)
MachineType: ASUS System Product Name
ProcKernelCmdLine: BOOT_IMAGE=/boot/vmlinuz-6.8.0-41-generic root=UUID=6fe1f015-c88c-47ad-8b06-2ddd0ce2fc05 ro quiet splash vt.handoff=7
SourcePackage: xorg
Symptom: display
UpgradeStatus: Upgraded to noble on 2024-06-03 (80 days ago)
dmi.bios.date: 10/27/2021
dmi.bios.release: 12.3
dmi.bios.vendor: American Megatrends Inc.
dmi.bios.version: 1203
dmi.board.asset.tag: Default string
dmi.board.name: Z590 WIFI GUNDAM EDITION
dmi.board.vendor: ASUSTeK COMPUTER INC.
dmi.board.version: Rev 1.xx
dmi.chassis.asset.tag: Default string
dmi.chassis.type: 3
dmi.chassis.vendor: Default string
dmi.chassis.version: Default string
dmi.modalias: dmi:bvnAmericanMegatrendsInc.:bvr1203:bd10/27/2021:br12.3:svnASUS:pnSystemProductName:pvrSystemVersion:rvnASUSTeKCOMPUTERINC.:rnZ590WIFIGUNDAMEDITION:rvrRev1.xx:cvnDefaultstring:ct3:cvrDefaultstring:skuSKU:
dmi.product.family: To be filled by O.E.M.
dmi.product.name: System Product Name
dmi.product.sku: SKU
dmi.product.version: System Version
dmi.sys.vendor: ASUS
version.compiz: compiz N/A
version.libdrm2: libdrm2 2.4.120-2build1
version.libgl1-mesa-dri: libgl1-mesa-dri 24.0.9-0ubuntu0.1
version.libgl1-mesa-glx: libgl1-mesa-glx 23.0.4-0ubuntu1~23.04.1
version.xserver-xorg-core: xserver-xorg-core 2:21.1.12-1ubuntu1
version.xserver-xorg-input-evdev: xserver-xorg-input-evdev N/A
version.xserver-xorg-video-ati: xserver-xorg-video-ati N/A
version.xserver-xorg-video-intel: xserver-xorg-video-intel N/A
version.xserver-xorg-video-nouveau: xserver-xorg-video-nouveau 1:1.0.17-2build1