FOR /F "tokens=*" %%F IN ('dir /b *.heic') DO (
    rem Converter HEIC para PNG com nomes diferenciados
    ffmpeg -i "%%F" -map 0 "%%~nF_%%d.png"
    
    rem Criar mosaico de imagens em um único arquivo PNG
    ffmpeg -i "%%~nF_%%d.png" -vf "tile=8x6" "%%~nF.jpg"
        
    del %%~nF_*.png
    rem del %%F
)

This DOS script converts all HEIC photos for IPHONE 12 pro in the current directory.
Comment out the last line if you want to exclude the original files.
PS 1: A border is set around because it is acctually in the file, but is not shown in the HEIC version.
PS 2: Guess you may need to adjust the TILE option in case your photo is from another IPHONE version,