While I understand your frustration, you’re incorrect about requiring a theme that is 5 years old … the oldest theme for WP Job Manager isn’t even 5 years old, so that statement is incorrect.
On top of that, the themes for WP Job Manager are actively developed and updated, and actually Jobify just released a new update today.
If you want a custom or to customize a template, it can be modified via template overrides and are easy to do, there is plenty of documentation on the wpjobmanager.com site for this.
What conflicts are you referring to that this plugin has (theme or plugin)? I haven’t heard of any major conflicts and i’ve been developing plugins for WPJM for the past 2+ years.
While support may be lacking on the WP forums, the github repository is actively monitored and receives responses and updates on issues frequently …. just sayin …