Update:
I bought a new motherboard+CPU+accessories, the card 9060 is now working properly with drm-612-kmod built from ports + necessary firmware packages. Resizable SAM in BIOS is enabled. I did not try to disable it yet. If anyone is interested, I may try it.
Code:
[I] ~ $ pkg info | grep firmware
gpu-firmware-amd-kmod-dcn-3-1-5-20260519.1501000 Firmware modules for dcn_3_1_5 AMD GPUs
gpu-firmware-amd-kmod-dcn-4-0-1-20260519.1501000 Firmware modules for dcn_4_0_1 AMD GPUs
gpu-firmware-amd-kmod-gc-10-3-6-20260519.1501000 Firmware modules for gc_10_3_6 AMD GPUs
gpu-firmware-amd-kmod-gc-12-0-0-20260519.1501000 Firmware modules for gc_12_0_0 AMD GPUs
gpu-firmware-amd-kmod-kaveri-20250109.1501000 Firmware modules for kaveri AMD GPUs
gpu-firmware-amd-kmod-psp-13-0-5-20260519.1501000 Firmware modules for psp_13_0_5 AMD GPUs
gpu-firmware-amd-kmod-psp-14-0-2-20260519.1501000 Firmware modules for psp_14_0_2 AMD GPUs
gpu-firmware-amd-kmod-sdma-5-2-6-20260519.1501000 Firmware modules for sdma_5_2_6 AMD GPUs
gpu-firmware-amd-kmod-sdma-7-0-0-20260519.1501000 Firmware modules for sdma_7_0_0 AMD GPUs
gpu-firmware-amd-kmod-smu-14-0-2-20260519.1501000 Firmware modules for smu_14_0_2 AMD GPUs
gpu-firmware-amd-kmod-vcn-3-1-2-20260519.1501000 Firmware modules for vcn_3_1_2 AMD GPUs
gpu-firmware-amd-kmod-vcn-5-0-0-20260519.1501000 Firmware modules for vcn_5_0_0 AMD GPUs
wifi-firmware-ath12k-kmod-wcn7850_hw20-20251125 Firmware modules for the ath12k (wcn7850_hw20) WiFi NIC driver
[I] ~ $ pkg info | grep drm
drm-612-kmod-6.12.85.1501000_1 Direct Rendering Manager (DRM) GPU drivers
drm_info-2.10.0 Dump info about DRM devices
libdrm-2.4.133,1 Direct Rendering Manager library and headers
[I] ~ $ pciconf -lv | grep -B3 display
vgapci0@pci0:3:0:0: class=0x030000 rev=0xc0 hdr=0x00 vendor=0x1002 device=0x7590 subvendor=0x1043 subdevice=0x0639
vendor = 'Advanced Micro Devices, Inc. [AMD/ATI]'
device = 'Navi 44 [Radeon RX 9060 XT]'
class = display
Note: do not be confused by these:
dcn_3_1_5, gc_10_3_6, psp_13_0_5, sdma_5_2_6, vcn_3_1_2
those were for my integrated radeon graphics card, which is now disabled in BIOS. The RX9060 does not work when the integrated card is enabled in BIOS, kdldloading amdgpu leads to some kind of confusion and reboot (unsuprisingly, the computer does not know which card do I want).