Should I stop using Version 1.4 on WordPress 4.9.x?

Hello. Recently I noticed that Version 1.4 no longer supports WordPress 4.9. My blogs run on WordPress 4.8.x or 4.9.x. On the surface, the plugin seems to be working fine on them, but do I have to stop using Version 1.4 of this plugin for these blogs?

Also, should I NOT install the present Version 1.4 on a new blog running on WordPress 4.9.x?

If I have to stop using it, where can I find its lower versions?

Thank you.