Tetrahedron Net (general)
This is a general tetrahedron with any triangular faces.
On the left, drag C to change the shape of the middle triangle. Drag D to change another face. Then drag E to see how the remaining 2 faces can be adjusted.
On the right, drag D, E and F to fold the shape in order to make a tetrahedron.
You may try another version, with focus on the apex and altitude:
https://www.geogebra.org/m/wdkbbq49