I have RX 580 graphics card. When i try to render my video with "hardware acceleration" option in render menu, there is a red "X" in VAAPI AMD. I use Manjaro. Any ideas?

When i try to render by VAAPI AMD it says:

mlt_repository_init: failed to dlopen /usr/lib/mlt-7/libmltsox.so (libsox.so.3: cannot open shared object file: No such file or directory) No LADSPA plugins were found! Check your LADSPA_PATH environment variable. mlt_repository_init: failed to dlopen /usr/lib/mlt-7/libmltrubberband.so (librubberband.so.2: cannot open shared object file: No such file or directory)
mlt_repository_init: failed to dlopen /usr/lib/mlt-7/libmltsdl.so (libSDL-1.2.so.0: cannot open shared object file: No such file or directory)
mlt_repository_init: failed to dlopen /usr/lib/mlt-7/libmltrtaudio.so (librtaudio.so.6: cannot open shared object file: No such file or directory)
mlt_repository_init: failed to dlopen /usr/lib/mlt-7/libmltmovit.so (libmovit.so.8: cannot open shared object file: No such file or directory)
mlt_repository_init: failed to dlopen /usr/lib/mlt-7/libmltopencv.so (libopencv_tracking.so.406: cannot open shared object file: No such file or directory)
[h264_vaapi @ 0x7fac0c201f40] Driver does not support some wanted packed headers (wanted 0xd, found 0). [h264_vaapi @ 0x7fac0c201f40] Driver does not support packed sequence headers, but a global header is requested. [h264_vaapi @ 0x7fac0c201f40] No global header will be written: this may result in a stream which is not usable for some purposes (e.g. not muxable to some containers). [h264_vaapi @ 0x7fac0c201f40] Hardware does not support encoding at size 3216x4288 (constraints: width 0-4096 height 0-2304).

From the errors, you are missing some libraries, namely related to rtaudio, movit, opencv, and SDL.
You will need to install whatever Manjaro packages that provide these.