Legacy Extensibility
While UXP is the recommended platform for all plugin developers to build on, Photoshop 2022 continues to support legacy extensibility features.
ExtendScript
The UXP Photoshop DOM API aims to be the evolution of the ExtendScript DOM. There are currently no plans to remove ExtendScript support from Photoshop.
Even though the ExtendScript Toolkit IDE is no longer maintained due to its reliance on 32-bit architectures, you can develop ExtendScripts using the Visual Studio plugin for ExtendScript.
ExtendScript developers wishing to migrate their plugins onto the UXP platform should consult the UXP for ExtendScript Developers.
CEP (Common Extensibility Platform)
The Common Extensibility Platform, introduced as a way of extending Creative Suite applications, will continue to be supported in Photoshop.
CEP developers wishing to migrate their plugins onto the UXP platform should consult the UXP for CEP Developers.
Native C++ Plugins
Plugins using native C++ are an important part of the Photoshop extensibility ecosystem and will continue to be supported.
A communication bridge suite was created to allow C++ plugins running under Photoshop to communicate with UXP plugins. See Communication with C++ Plugin SDK.
