It was Apple's decision 18 months ago to only support 64-bit apps with the release of macOS Catalina.
As Adobe Photoshop Elements 2018 was released 3.5 years ago and contains some 32-bit code, unfortunately that version is no longer compatible with the latest macOS. You will need to upgrade to the latest Adobe Photoshop Elements 2021 release. The standard price for the upgrade is around $80.
Before you update your OS or buy a new computer (especially macOS and Apple Mac computers) you should always check first to see whether your existing apps will be compatible.