This is not simple to bump as the architecture was completely changed with the rewrite/release of modsecurity 3.x.
Package is now split in:
* libmodsecurity (https://github.com/SpiderLabs/ModSecurity), web server agnostic and better performing
* ModSecurity-Apache connector to interface between Apache and libmodsecurity (https://github.com/SpiderLabs/ModSecurity-apache)
Latest version of 2.x is v2.9.3 which is available in the Gentoo tree. There are a few upstream changes pending for v2.x: https://github.com/SpiderLabs/ModSecurity/blob/v2/master/CHANGES
According to https://coreruleset.org/installation/ version 2.9.x is still recommended for Apache.