If you have a legitimate, paid CS4 serial number from back in the day, you can contact Adobe Support. They have a legacy downloader for paying customers who need to reinstall their old software. You cannot get the trial this way, but you can get the full version you paid for.
For the safest and most efficient workflow, it is recommended to use the for the latest features, or switch to free alternatives like Photopea or GIMP . These options will keep your computer secure while providing you with powerful editing tools. photoshop cs4 trial download