Specify the maximum count of parameters instead of number of bytes
i.e.
GLint iscol;
GL.glGetInternalformativ(target, fmt, eGL_DEPTH_COMPONENTS, sizeof(GLint), &isdepth);
becomes
GL.glGetInternalformativ(target, fmt, eGL_DEPTH_COMPONENTS, 1, &isdepth);
From GL references pages: https://www.khronos.org/registry/OpenGL-Refpages/gl4/html/glGetInternalformat.xhtml
bufSize
Specifies the maximum number of integers of the specified width that may be written to params by the function.