Can I migrate the existing plugin to UXP or do I have to write it from scratch?

[Roman5FD8]

Hello everyone!

I have a photoshop plugin that works in almost all versions of Photoshop untill 2020.
Recently I tried my plugin on Photoshop 2021 and it didn't work. After reading this article I decided to convert my plugin to UXP.
My question is

1.  Can I migrate the existing plugin or do I have to write it from scratch?
2. And if I can migrate the existing one will it be supported by previous versions of Photoshop?

I hope this is the right place to ask) 
Thanks.