Encoder, decoder, encoding method, and decoding method

A non-transitory storage medium storing a bitstream and a program having instructions for transmission thereof, the bitstream including information according to which a decoder performs a decoding process, wherein

• in a first decoding process, a current block is inverse-quantized using a first quantization matrix in both of a first case where an inverse primary transform is performed on the current block and an inverse secondary transform is not performed on the current block and a second case where both the inverse primary transform and the inverse secondary transform are performed on the current block,
• in a second decoding process, the current block is inverse-quantized using a second quantization matrix in a third case where the inverse primary transform is performed on the current block and the inverse secondary transform is not performed on the current block,
• in a third decoding process, the current block is inverse-quantized without using a quantization matrix in both of a fourth case where both the inverse primary transform and the inverse secondary transform are skipped for the current block and a fifth case where both the inverse primary transform and the inverse secondary transform are performed on the current block,
• the inverse primary transform corresponds to an orthogonal transform, and the inverse secondary transform corresponds to a low-frequency non-separable transform (LFNST), and
• when the inverse secondary transform is performed on the current block, the inverse secondary transform is performed on the current block in a region of a first size smaller than a size of the current block.