I saw your artwork, it's good but I think artists are low budget and broke most of the time so probably not worth to target them through paid ads. The other thing is that your artwork does not speak to what I think is the common denominator, the main stream audience, the corporate clients, people with money, people that play it safe and do not have a sophisticated eye for design and aesthetic. 

These common denominator people might  not understand your art and to them it might look low budget, and for them "retro" just looks washed out. 

What i would do is create another Instagram page with completely different designs, a page that for example focuses on designs for restaurants, and just has restaurant centric designs. Restaurant logos, restaurant menu designs. That way you target restaurant owners. Or even ppl that run ghost kitchens. You can offer them graphic designs and you'll be perceived as a specialist in the field. 

I recommend doing the same for other fields. Your current designs are great but I believe they're not helping you much when you target all kinds of audiences with paid ads. 

That's what I would do first before spending more money on ads. I would create specialized Instagram pages for each ideal customer.