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I changed from a version of Windows that is not supported any more to Ubuntu 20.04.0. This laptop is connected to a TV monitor with a VGA cable (xrandr calls it VGA-1). The laptop does not have a HDMI port. I have had no issues on Windows with this cable at the same resolution and framerate. This issue happens only on Gnome, not Wayland. From the current state of Wayland, using it is not feasible.

The problem is that when I log in to a user (after a restart, or after logout), the laptop screen sometimes shows a black screen with the cursor flashing once every 0.5 seconds (best guess at timing). At this time, the secondary display flickers at the same rate between a black screen and no signal.

Sometimes the flickering stops after around 3 seconds and the desktop shows on the laptop monitor. Other times, the flickering continues indefinitely. I have tried pressing super+1 to open the first application (gedit) in the dock while it is flashing. gedit is not open when I disconnect the cable. Pressing super+1 after I can see the desktop opens gedit as expected.

The flickering can be temporarily fixed (until the next time the problem occurs after trying to log into a user) by disconnecting the VGA cable and reconnecting it. After reconnecting the cable, the desktop does the "popup" animation (expand from single point at center of screen to the whole monitor). This is regardless of how long I wait before disconnecting and reconnecting the cable.

The flickering does not happen at all when I log into a user if the VGA cable is not connected.

I have tried with and without fractional scaling (both at 100%) in single monitor mode on both laptop and TV display. The laptop resolution is 1440x1900 at 60 FPS and the TV resolution is 1280x720 at 60 FPS.

What can I do to prevent the "flickering indefinitely" while still being able to use the "single display" mode (on laptop monitor xor TV monitor)?

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I also had some flickering problems with a fresh isntall of ubuntu 20.04 (see Ubuntu screen flickering). Could you try to use Wayland display server on the logging screen: click your profile > click the white weel in lower right corner > choose 'Ubuntu on Wayland' and see if it is better ?

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Maybe problem with the display driver, in ubuntu, I don't know if you can reinstall drivers because drivers are inside the kernel executable.

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