As Incanta says, it depends on the plugin code. Mine transfer easily, others’ like DoN’s Meshpainting require big changes I can’t be bothered to take care of myself. And if the marketplace doesn’t offer a structure to distribute the plugins on UE5 to those who purchased the plugin, we don’t really have an option to distribute even if we upgrade for UE5 right now.
Your best option as an individual user right now is to contact individual authors or recompile the plugins you use yourself and fix issues as they come up. I’ve started a thread to help people upgrade their C++ code to UE5: Ue5 C++ Upgrade Tips. You can use it to help you fix issues in plugins when migrating.
For my part, since iTween is free I’ll be upgrading it and posting a UE5 version soon, but for Runtime DataTable and easyCSV buyers will have to contact me directly to get a Windows dev version.
iTween : Free, smooth, procedural object animation
easyCSV : Read data from any CSV and put them in an easy-to-access string map!
Runtime DataTable : Import and export game data to and from CSV or Google Sheets while your game is running!