phpList 3.5.x with old API v1 plugin - will it work?

Question: Can I upgrade phpList to 5.6.x, keep the new API disabled, run on PHP 7.3, and still use the old plugin API from 2017 so I won’t have to change my working site code?

Background: I was running phpList 3.3.x on my old server and had invested a lot of time in 2017 getting the old v1 API plugin working so my customers can subscribe, change their email address, unsubscribe, and be subscribed invisibly when they set up an account by just checking a box during account setup. I recently moved to a new server that is running PHP 7 and I need to update my site code and would like to update phpList to 5.6.x. but I’ve been reading a bunch of posts here that say the new built-in API offers less functionality than the old plugin, plus people are having trouble getting it working - and the doc is extremely minimal, especially since I don’t use JSON and am not fluent in it. I really don’t want to spend a ton of time trying to get the new API working, so I’d like to just use the old v1 plugin API - if it will work with phpList 5.6.x.

Thanks for any light than can be shed on this,