Unfortunately, upstream IceCat appears to use the FireFox 60.x ESR branch, which is three branches behind the current ESR and is past its end-of-life date. It's also a few security updates behind the 60.x ESR branch's last release.
The GUIX package is more recent, but its description states:
> WARNING: IceCat 91 has not yet been released by the upstream IceCat project. This is a preview release, and does not currently meet the privacy-respecting standards of the IceCat project.
https://www.gnu.org/software/gnuzilla/
It seems it is mostly maintained within GNU Guix now (which has 91.3.0).
[^]: It comes with its own set of opinionated (but privacy-friendly) add-ons.