Engagement will take time! Yes it will be harder after four years without it, but you can do it. Just recognize that it's going to take more than two sessions, or two weeks, or two months, etc.
First consider the environment. Are you trying this at home or out at a park somewhere? Starting at home is usually easier because the environment is already familiar. As your dog gets better at home, then start taking it on the road. But again try not to increase the environmental challenges too suddenly. Start with a park at a quiet time before trying a busy time.
The leash. I admit I didn't watch the whole video so I don't know if this was discussed, but the leash in that video is too long for just starting out. I'd start with a regular six foot leash to limit how much space the dog has to roam. Limiting the dog's space increases the chances that he'll check in with you, because that six foot radius becomes boring much faster than a 10' or 20' radius.
Two things that also help a lot with engagement: rewarding instead of bribing, and using a verbal release cue to end the engagement. Make sure you're rewarding (mark and then feed/show the toy) instead of bribing (showing the food/toy to entice the dog to you). It's a fine difference to us, huge difference to the dog and bribing is often the first thing that makes engagement fail. Then, when the dog is focused on you, use a verbal release cue (such as "all done", "that'll do", "go sniff", etc) to release the dog back to the environment. Keep the duration of engagement very short at first, to build on the dog's ability to be successful and stay engaged until released. Yes there will be times your dog checks out without the release, but over time that should decrease.
To be honest, I wouldn't worry too much about ball drive. Some trainers get fixated on it (especially in our GSD world) but it's not really necessary. For engagement you have to use what the dog already finds reinforcing, and if the ball isn't reinforcing then you have to work on that separately, and it's up to you if that is worth it or not.
For a free resource, Denise Fenzi has written a lot of blog posts about engagement: https://denisefenzi.com/?s=engagement
For paid resources, I really like the stuff by Forrest Micke and Michael Ellis, which you can find on Leerburg.