La roche posay has a new range called Mela B3 that stops dark matks and fades existing one.
I’ve had microneedling and microdermabrasion in the past and it’s really helped but you do have to be consistent and it can get quite expensive.
Vitamin c is a great shout - I’ve heard a vitamin C powder is better/more effective than the serums and creams out there as they lose potency when exposed to oxygen I believe or perhaps i’ts light but either way you use a small amount of powder with some moisturiser or serum and its meant to be more effective - am currently trying but it’s too early to tell.
Any products with vitamin C should help.