Multiwfn *perfectly* supports IGM method, please check Section 3.23.5 of the manual for introduction and Section 4.20.10 for examples.

There have been about ten published papers that performed the IGM analysis using Multiwfn:

Capturing methanol and dimethoxymethane gases with ionic liquids
Chalcogen−substitution modulated supramolecular chirality and gas sensing properties in perylenediimides
Chemical Kinetics of H-Atom Abstraction from Ethanol by HȮ2-Implication for Combustion Modeling
Effects of noncovalent interactions on the impact sensitivity of HNS-based cocrystals-A DFT study
Investigation of ECD conformational transition mechanism of GLP-1R by molecular dynamics simulations and Markov State Model
Liquid–Liquid Extraction of Benzene Using Low Transition Temperature Mixtures-COSMO-SAC Predictions and Experiments
Role of water in the reaction mechanism and endo-exo selectivity of 1,3‐dipolar cycloadditions elucidated via quantum chemistry and machine learning
Structure and Interaction of Ionic Liquid Monolayer on Graphite from First Principles
The Interaction between Chitosan and Tannic acid Calculated Based on the Density Functional Theory