var PanelTestText = container.Add(new CuiPanel
                    {
						Image  =
                {
                    Color = "0.1 0.1 0.1 1"
                },
                        RectTransform =
                {
                    AnchorMin = "0.287 0.38",
                    AnchorMax = "0.717 0.48"
                },
				CursorEnabled = true
                    }, "Main");
					
			container.Add(new CuiElement
                    {
                        Name = "TestText",
						Parent = PanelTestText,
                        Components = {
                            new CuiInputFieldComponent {
                                Text = "TEXT",
								Command = "example.exampleinputtextcb",
								Font = "robotocondensed-regular.ttf",
								FontSize = 20,
								Align = TextAnchor.MiddleLeft,
								Color =  "0.1 1 0.4",
								IsPassword = false,
								CharsLimit = 75
                            },
                            new CuiRectTransformComponent {
                                 AnchorMin = "0 0",
								 AnchorMax = "1 1"
                            }
                           }
                    });

How to make a CuiPanel a parent for Input?

Just pass "PanelTestText" in as the parent and it should work.

Also there isn't a cui layer called "Main", maybe you meant "Hud" or "Overlay"? Unless I'm mistaken and that is the name of another cui element.

I did it but i still can't find input.

string PanelTestText = "PanelTest";
			container.Add(new CuiPanel
                    {
						Image  =
                {
                    Color = "0.1 0.1 0.1 1"
                },
                        RectTransform =
                {
                    AnchorMin = "0.287 0.38",
                    AnchorMax = "0.717 0.48"
                },
				CursorEnabled = true
                    }, $"Overlay", PanelTestText);
					
			container.Add(new CuiElement
                    {
                        Name = "TestText",
						Parent = PanelTestText,
                        Components = {
                            new CuiInputFieldComponent {
                                Text = "TEXT",
								Command = "example.exampleinputtextcb",
								Font = "robotocondensed-regular.ttf",
								FontSize = 20,
								Align = TextAnchor.MiddleLeft,
								Color =  "0.1 1 0.4",
								IsPassword = false,
								CharsLimit = 75
                            },
                            new CuiRectTransformComponent {
                                 AnchorMin = "0 0",
								 AnchorMax = "1 1"
                            }
                           }
                    });​

Strange, since the code you just sent seems to work for me.