Hundrends of millions have been invested in this feat, after some initial promise such as the Ashtekar's reformulation of GR, the Wheeler DeWitt equation etc (i. E. 100m to a research Group baseb on Imperial college, UK in early '00s).Reseasrch however cumilated to weird theories such as Loop Quantum theory that lost traction by the early'2020s.
Now research is based on 3 premises
GR focused
** diffeomorphism invariance (aborting the meaning of some SR results)
** shape dynamics
QM focused
** restoring locality if the wavefunction update if seen as physical process