If you're already working in their systems and domain, you probably have a decent idea of how you can address it, even if it's outside your main area of expertise. This happens to me, and... if I'm completely unqualified, I just say "I can't do that, here's someone else who can" and make a referral/connection to someone in my network. That's often the harder part - finding someone in my network who is both competent and available.
I know a few very experienced people who have looked into contracting or freelancing over the past year either for the first time or for the first round in many years. They have good skills and the aptitude to pick up whatever else they need, but without the broad network that comes with years of doing short term gigs, they've found the market very tough to break into. I doubt they would recognise the talk of a seller's market and ever-increasing rates that we see on sites like HN!
If you don't have that network and people actively seeking you out, you get stuck with looking via agencies (= ghosted often if you don't already have exactly the right buzzwords) or the online marketplaces (= low rates, poor quality clients and high risk of problems with the marketplace itself). And even if you do, I've seen more than one person whose whole network basically all fell apart around the same time because whole industries were hit by COVID.
Today even more than usual, it is about who you know as much as what you know.
I think ML is probably different, in that it's not something that can be just 'picked up' that easily (AFAICT).
But it's honestly surprised me over the years how often my clients have said "Hey, I know it's not your main area of competence, but do you reckon you could have a go at this?"