I believe you are using the On-Premise version of Orchestrator. The scheduled deprecation date for both Standard Machine & Classic Folder is October 2022. However, its interesting to note that Deprecation does not mean removal. It may so that these features will be removed from 2022.10 which will be released in October 2022 (but it’s highly unlikely).
Also, even if they happen to remove the features in question from 2022.10. Since you are on-premise let’s say you are on version 2020.10 or 2021.10, useless you do an upgrade to 2022.10 everything will work as expected.
Overall, there is no need to rush with the Modern Folder Migration. That said, I recommend you move all the existing processes to modern folder first and once everything is migrated to Modern Folder start working on the new process.
Currently you can use the classic folder, but as uipath suggested new process should be done in the Modern Folder as classic version is going to depreciate. Otherwise you will have to put more efforts for migrating everything to Modern from classic folders.
So better as you mentioned Migrate the ongoing process to Modern folder and create the new process to Modern folder directly.