Slow seedling growth with led sunlight

Weil das Licht nicht genügt, würde ich mal vermuten. Falsches Spektrum und die Fensterscheibe filtert das Sonnenlicht zu stark. Die Erde könnte auch falsch sein, aber ohne detailliertere Informationen, kann Dir niemand helfen. Mach am besten Bilder, beschreib Dein Medium und dann stell Deine Frage erneut. Viel Glück!

I recommend that you give your seedlings water once and then let the soil dry out, in this way the roots will have a chance to breathe and will not drown in permanently wet soil. Be patient, young seedlings do not grow at the speed of well-formed ones!

With 9x9 Watts you might think that would add up to a 100 watt or near it. But that's not the case. All you are doing with 9x is making the surface area bigger. Even with them close together it wouldn't have a big impact on highering your par. Y don't you just buy a cheap 100watt led of amazon you'll c the ppfd map 900+ ppfd you'll be able to get for 40-50$. Good luck.

Often sprouts seem to take a pause after emerging from the ground. I think they get the first leaves then focus more on root growth so it can seem the plant has stopped growing or is growing slow. Give is several more days+ and I think you will notice new growth.

Not enough wattage and likely temps are not warm enough

9 x 9W lights ain't gonna set the world on fire.......... Cool/cold temps will slow growth, Full moon will also slow above ground growth, believe it or not. 5 days is not a long time to wait for seedlings.