The only error shown in /var/log/boot.log:
[FAILED] Failed to start Load/Save Screen Backlight Brightness of backlight:acpi_video0.
See 'systemctl status systemd-backlight@backlight:acpi_video0.service' for details.

which I solved with the command: 
systemctl mask systemd-backlight@backlight:acpi_video0.service

With kernel 5.8.18 I still see the earlier mentioned errors and warnings. Not sure if this means less performance in 3D applications?

$ sudo dmesg --level=err,warn
[    0.318622] TSC synchronization [CPU#0 -> CPU#1]:
[    0.318622] Measured 453215862 cycles TSC warp between CPUs, turning off TSC clock.
[    0.318622]   #2  #3  #4  #5  #6  #7  #8  #9 #10 #11 #12 #13 #14 #15
[    2.666156] pci 0000:00:00.2: AMD-Vi: Unable to read/write to IOMMU perf counter.
[    2.666298] pci 0000:00:00.2: can't derive routing for PCI INT A
[    2.666299] pci 0000:00:00.2: PCI INT A: not connected
[    2.667642]  PPR X2APIC NX GT IA GA PC GA_vAPIC
[    2.737746] i8042: PNP: PS/2 appears to have AUX port disabled, if this is incorrect please boot with i8042.nopnp
[    2.740046] platform eisa.0: EISA: Cannot allocate resource for mainboard
[    2.740048] platform eisa.0: Cannot allocate resource for EISA slot 1
[    2.740049] platform eisa.0: Cannot allocate resource for EISA slot 2
[    2.740049] platform eisa.0: Cannot allocate resource for EISA slot 3
[    2.740049] platform eisa.0: Cannot allocate resource for EISA slot 4
[    2.740050] platform eisa.0: Cannot allocate resource for EISA slot 5
[    2.740050] platform eisa.0: Cannot allocate resource for EISA slot 6
[    2.740051] platform eisa.0: Cannot allocate resource for EISA slot 7
[    2.740051] platform eisa.0: Cannot allocate resource for EISA slot 8
[    2.798587] Unstable clock detected, switching default tracing clock to "global"
               If you want to keep using the local clock, then add:
                 "trace_clock=local"
               on the kernel command line
[    2.962855] i2c_hid i2c-ITE8227:00: supply vdd not found, using dummy regulator
[    2.962885] i2c_hid i2c-ITE8227:00: supply vddl not found, using dummy regulator
[    2.964303] acpi PNP0C14:01: duplicate WMI GUID 05901221-D566-11D1-B2F0-00A0C9062910 (first instance was on PNP0C14:00)
[    2.964386] acpi PNP0C14:02: duplicate WMI GUID 05901221-D566-11D1-B2F0-00A0C9062910 (first instance was on PNP0C14:00)
[    2.979559] nvme nvme0: missing or invalid SUBNQN field.
[    3.275362] i2c_hid i2c-MSFT0001:00: supply vdd not found, using dummy regulator
[    3.275383] i2c_hid i2c-MSFT0001:00: supply vddl not found, using dummy regulator
[    4.346318] snd_pci_acp3x 0000:03:00.5: Invalid ACP audio mode : 0
[    4.370739] ACPI Error: No handler for Region [ECSI] (000000005ff1a6f4) [EmbeddedControl] (20200528/evregion-127)
[    4.371044] ACPI Error: Region EmbeddedControl (ID=3) has no handler (20200528/exfldio-261)
[    4.371290] No Local Variables are initialized for Method [ECRD]
[    4.371292] No Arguments are initialized for method [ECRD]
[    4.371302] ACPI Error: Aborting method \_SB.UBTC.ECRD due to previous error (AE_NOT_EXIST) (20200528/psparse-529)
[    4.371582] ACPI Error: Aborting method \_SB.UBTC._DSM due to previous error (AE_NOT_EXIST) (20200528/psparse-529)
[    4.371890] ACPI: \_SB_.UBTC: failed to evaluate _DSM (0x6)
[    4.371898] ucsi_acpi USBC000:00: ucsi_acpi_dsm: failed to evaluate _DSM 2
[    4.442211] iwlwifi 0000:01:00.0: Direct firmware load for iwlwifi-cc-a0-56.ucode failed with error -2
[    4.442371] iwlwifi 0000:01:00.0: Direct firmware load for iwlwifi-cc-a0-55.ucode failed with error -2
[    4.442408] iwlwifi 0000:01:00.0: Direct firmware load for iwlwifi-cc-a0-54.ucode failed with error -2
[    4.442428] iwlwifi 0000:01:00.0: Direct firmware load for iwlwifi-cc-a0-53.ucode failed with error -2
[    4.442551] iwlwifi 0000:01:00.0: Direct firmware load for iwlwifi-cc-a0-52.ucode failed with error -2
[    4.442581] iwlwifi 0000:01:00.0: Direct firmware load for iwlwifi-cc-a0-51.ucode failed with error -2
[    4.442603] iwlwifi 0000:01:00.0: Direct firmware load for iwlwifi-cc-a0-50.ucode failed with error -2
[    4.442708] iwlwifi 0000:01:00.0: Direct firmware load for iwlwifi-cc-a0-49.ucode failed with error -2
[    4.445956] iwlwifi 0000:01:00.0: Direct firmware load for iwl-debug-yoyo.bin failed with error -2
[    4.603172] acp_pdm_mach acp_pdm_mach.0: snd_soc_register_card(acp) failed: -517
[    4.603260] acp_pdm_mach acp_pdm_mach.0: snd_soc_register_card(acp) failed: -517
[    4.812215] thermal thermal_zone0: failed to read out thermal zone (-61)
[    5.498758] ucsi_acpi: probe of USBC000:00 failed with error -5
[    5.572192] kauditd_printk_skb: 31 callbacks suppressed
[    5.623264] [drm:dm_helpers_dp_write_dpcd [amdgpu]] *ERROR* Failed to find connector for link!
[    5.623920] [drm:dm_helpers_dp_write_dpcd [amdgpu]] *ERROR* Failed to find connector for link!
[    5.624513] [drm:dm_helpers_dp_write_dpcd [amdgpu]] *ERROR* Failed to find connector for link!
[    5.949908] iwlwifi 0000:01:00.0: FW already configured (0) - re-configuring
asterix@Idefix:~$