Non-commercial as long as you don't sell them and just present them on YouTube.

I'm using my customs for a Product on LEGO Ideas - commercial or not?

Wait, I'm making them with my own Blender Add-on, so I don't think I need to ask you. Nvrmind XD

When you exported your model from Mecabricks, you had to agree to the user conditions. All assets exported from Mecabricks remain the property of Mecabricks and cannot be redistributed or use for commercial purposes. There is an exception for custom textures that remain the property of the creator.

However you could also read that LEGO Ideas projects are exempted. So yes you can use images generated with Mecabricks assets for your LEGO Ideas projects without asking for permission.

thanks