I’d make sure to maintain protein as well.
Weight loss is calories in v calories out.
When I started, I saw FTP gains as well as weight loss, but later down the line I could only maintain FTP while losing weight. I’m now aware I wasn’t fuelling workouts and recovery enough (too much dieting on the bike), but I still think it would be difficult to significantly grow FTP in a significant deficit. I think one has to be the primary goal.
If I was going again, I’d use a percentage based deficit rather than a specific calorie deficit, as I think that definitely contributed to under fuelling and therefore slowing training progress, even if weight loss goals were achieved. But to be fair to myself, weight loss was my primary goal.