I’ve had similar results. I went from 209 to 256 through SSB1 and 2. I’ve since come back to 240ftp through my build phase. However, I’ve increased my running quite a bit so I’m happy with where I’m at.
If you’re untrained or new to regular training, just getting on the turbo and pedalling for an hour a few times a week is going to make you fitter. As you get better, the gains are a little harder to come by.
As for motivation, make sure you connect that motivation to real-world goals - whether that’s racing, completing a 100 mile sportive, getting PRs on Strava segments, losing weight, going on a bikepacking holiday somewhere, getting a great cyclist’s tan, whatever gets you back on the bike. Don’t let your FTP be your primary source of motivation.
The purpose of your FTP is merely to scale your workouts to your abilities. No matter your FTP, they should feel equally hard. But FTP is not on the only measure of performance, and reading your post, I’d rather say you should make you to have more fun on the bike. Training is not an end in itself, so perhaps you need to get outdoors more often? Or ride with others?