Because of a new installation of HCL SafeLinx at customer I opened a case at HCL to get an information if CentOS 9.x also is supported due to the EOS date for CentOS 8.x Stream at Mai 31st 2024 and received the following information:

CentOS 9.x is supported, however it requires libxcrypt-compat package to be installed separately.

Product documentation for system requirement has been updated as well:
https://support.hcltechsw.com/csm?id=kb_article&sysparm_article=KB0104026

So it should be safe to use CentOS 9.x Stream for your HCL SafeLinx 1.4.x installation.