The version of JxBrowser in PAM 4.0 is 6.24.3 which uses Chromium 69. The same version is used in 3.4.4. Lower 3.4 releases use JxBrowser version 6.22.1.
The first release to include a newer JxBrowser version was 3.4.5, which included an update to JxBrowser 7.15. The same version is included in 4.0.1. In general you find the JxBrowser version used on the Third-Party License Acknowledgement page, e.g. here for 3.4.5.