It's better not to germinate in such a thing; the root will quickly show up against the walls, and due to the light, it will die off, and the plant will perish very quickly. There's no space, it's just a gimmick for germinating seeds, nothing more... well, or to record a timelapse video of how the root quickly fills this volume, the plant stretches strongly, the root darkens, the plant bends over, and dies... there are such videos on YouTube 👆
And it's best not to compact the substrate at all, so it stays loose and fine! 👌
Good luck, bro! ✊😇