Thinkpad T495s Ryzen，kubuntu 20.04：显示仅在恢复模式下工作

我刚刚在新的 thinkpad 495s 上重新安装了 kubuntu 20.04。

（图形）登录屏幕看起来很正常，只是缺少鼠标指针。但是，登录后，我的屏幕大多是黑色/灰色。启动控制台时（使用ctrl-alt-t），我可以从灰色中猜测它在那里，以便我可以输入sudo shutdown now.

但是，如果我用recovery模式开机，电脑几乎可以用了，只是我无法控制屏幕的背光：按fn-F5一下会弹出背光控制窗口，显示应该减少背光，但实际上没有任何反应。

编辑：显然，如果我在插入电源的情况下启动，显示器和背光都可以工作。

我不知道这两个问题是否相互关联。

martin@toolbox:~$ uname -r
5.4.0-45-generic

martin@toolbox:~$ lspci
00:00.0 Host bridge: Advanced Micro Devices, Inc. [AMD] Raven/Raven2 Root Complex
00:00.2 IOMMU: Advanced Micro Devices, Inc. [AMD] Raven/Raven2 IOMMU
00:01.0 Host bridge: Advanced Micro Devices, Inc. [AMD] Family 17h (Models 00h-1fh) PCIe Dummy Host Bridge
00:01.2 PCI bridge: Advanced Micro Devices, Inc. [AMD] Raven/Raven2 PCIe GPP Bridge [6:0]
00:01.3 PCI bridge: Advanced Micro Devices, Inc. [AMD] Raven/Raven2 PCIe GPP Bridge [6:0]
00:01.4 PCI bridge: Advanced Micro Devices, Inc. [AMD] Raven/Raven2 PCIe GPP Bridge [6:0]
00:01.7 PCI bridge: Advanced Micro Devices, Inc. [AMD] Raven/Raven2 PCIe GPP Bridge [6:0]
00:08.0 Host bridge: Advanced Micro Devices, Inc. [AMD] Family 17h (Models 00h-1fh) PCIe Dummy Host Bridge
00:08.1 PCI bridge: Advanced Micro Devices, Inc. [AMD] Raven/Raven2 Internal PCIe GPP Bridge 0 to Bus A
00:14.0 SMBus: Advanced Micro Devices, Inc. [AMD] FCH SMBus Controller (rev 61)
00:14.3 ISA bridge: Advanced Micro Devices, Inc. [AMD] FCH LPC Bridge (rev 51)
00:18.0 Host bridge: Advanced Micro Devices, Inc. [AMD] Raven/Raven2 Device 24: Function 0
00:18.1 Host bridge: Advanced Micro Devices, Inc. [AMD] Raven/Raven2 Device 24: Function 1
00:18.2 Host bridge: Advanced Micro Devices, Inc. [AMD] Raven/Raven2 Device 24: Function 2
00:18.3 Host bridge: Advanced Micro Devices, Inc. [AMD] Raven/Raven2 Device 24: Function 3
00:18.4 Host bridge: Advanced Micro Devices, Inc. [AMD] Raven/Raven2 Device 24: Function 4
00:18.5 Host bridge: Advanced Micro Devices, Inc. [AMD] Raven/Raven2 Device 24: Function 5
00:18.6 Host bridge: Advanced Micro Devices, Inc. [AMD] Raven/Raven2 Device 24: Function 6
00:18.7 Host bridge: Advanced Micro Devices, Inc. [AMD] Raven/Raven2 Device 24: Function 7
01:00.0 Network controller: Intel Corporation Wireless-AC 9260 (rev 29)
02:00.0 Non-Volatile memory controller: Samsung Electronics Co Ltd NVMe SSD Controller SM981/PM981/PM983
03:00.0 Ethernet controller: Realtek Semiconductor Co., Ltd. RTL8111/8168/8411 PCI Express Gigabit Ethernet Controller (rev 0e)
03:00.1 Serial controller: Realtek Semiconductor Co., Ltd. Device 816a (rev 0e)
03:00.2 Serial controller: Realtek Semiconductor Co., Ltd. Device 816b (rev 0e)
03:00.3 IPMI Interface: Realtek Semiconductor Co., Ltd. Device 816c (rev 0e)
03:00.4 USB controller: Realtek Semiconductor Co., Ltd. Device 816d (rev 0e)
04:00.0 Unassigned class [ff00]: Realtek Semiconductor Co., Ltd. RTS522A PCI Express Card Reader (rev 01)
05:00.0 VGA compatible controller: Advanced Micro Devices, Inc. [AMD/ATI] Picasso (rev d2)
05:00.1 Audio device: Advanced Micro Devices, Inc. [AMD/ATI] Raven/Raven2/Fenghuang HDMI/DP Audio Controller
05:00.2 Encryption controller: Advanced Micro Devices, Inc. [AMD] Family 17h (Models 10h-1fh) Platform Security Processor
05:00.3 USB controller: Advanced Micro Devices, Inc. [AMD] Raven USB 3.1
05:00.4 USB controller: Advanced Micro Devices, Inc. [AMD] Raven USB 3.1
05:00.5 Multimedia controller: Advanced Micro Devices, Inc. [AMD] Raven/Raven2/FireFlight/Renoir Audio Processor
05:00.6 Audio device: Advanced Micro Devices, Inc. [AMD] Family 17h (Models 10h-1fh) HD Audio Controller