Why do I have only about 30 fps with a GTX 1660 Ti with LOW shader (whichever) even though I've assigned Minecraft 6Gb Ram?

I've really tried everything and I'm really at the end.
Incidentally, I use Minecraft 1.12 (with Labymod) on every game I have the highest graphics settings liquid FPS except in Minecraft! I hear with many always the graphics card is the Probleim?
I also have Java 64bit. That's why I do not understand what else I could do. I thank EVERYONE who helps me.

I hope you also use a good DDR4 RAM, GPU and CPU seem to be good enough

MC Shader eats neatly, just make render distance a little bit down, make V sync and look obs is better

Go on graphics settings → Shader and say what you have right for settings in it.
How much FPS do you have if you do not have a shader inside?
What are the other graphics settings?

Yes twice 8 Gb DDr4

If you have 16GB RAM then give Minecraft 10GB quiet, then you have your rest!

I always think that Minecraft likes to deep fry the CPU and that could be the case with you. Your CPU is definitely not bad, but not too blatant. From the hardware it is the bottleneck. Did you make something yourself?

Yes I've reinstalled the whole pc. But I can play any game with the best graphics and good FPS.
I also just noticed that if I use in Mc Ultra shader I have about the same amount of FPS as if I use the low shader. I have about 40 fps but it is really very unstable and if I'm doing things like running, PVP or anything else. Are mostly bad drops. It sometimes goes down to 10fps or less.

Did you install the RAM correctly?

Well, I've already tried. Does not work because Minecraft anyway only 500 mb uses ka why

Yes they go without problems. (I've rebuilt everything into a new case and tested everything like other games and so on.

Go to the Nvidia graphics settings and see if you have frame rate limit set to 30, if it's not then go to program settings and choose Java and do the same thing.