IGraph/M 0.4 is released 
Please use only this version (or later) with Mathematica 12.1, as it brings many compatibility fixes.
The 0.4 series will be the last to offer compatibility with Mathematica 10.0. Starting with version 0.5, IGraph/M will only work with Mathematica versions supported by Wolfram Research. This means that the minimum required version will be Mathematica 11.0 or 11.1 (to be determined).
A web-based preview of the documentation is now available.