1. New growth is always soft

2. Black bamboo is not a house plant. What outdoor climate area are you in?

I live in a cool/wet climate in belgium so outdoors wont be so good rn because its cold and windy And rains alot here thats why its insidr atm until the new grown gets stronger

It's going to do poorly until it gets better light. Also, you shouldn't have pruned it as the leaves would have come back if it had more light. Bamboo does not regenerate branches or culms that are lopped off, so that stub is going to continue to look like that, although it should put out some leaves if you can improve the lighting. Bamboo can be grown indoors, but not easily, and there are some bamboo that can tolerate lower light than the one you have, so are better candidates for indoors.

The advantage of the species you have (presumably Phyllostachys nigra?) is that it can survive down to about -10C in a pot (-15C in the ground). It also likes water, and, as long as it's in a pot with drainage, a lot or rain won't hurt it. I live in the Seattle area where it's rainy, windy, and gray out for 4-5 of the winter months, and Belgium is probably no worse. I have a lot of bamboo species in the ground and at least a dozen different ones in pots, and they all stay leafy throughout the winter.

I think you are actually hurting your plant by keeping it inside, rather than protecting it. If you set it outside, it may not re-leaf much until it gets warmer, but I think it will be happier. The only downside is that severe, constant winds could cause leaf burn in the winter, but shouldn't otherwise damage the plant. The only thing that will hurt it in your climate is if the temperatures go below the ones I mentioned above. However, if it does get really cold, you could always bring the pot in for a day or two until the cold snap passes.

Thanks for the info. Its going to drop -10 around this time i will put it outside supported by a bamboostick after the big temperature drops.

1. What minimum temperature are you talking about (Centigrade or Fahrenheit)?

2. You could just push a simple stake into the pot and tie the floppy culm to it.

Celsius and yeah will be done thx