If your trying to convert an image you already have to look like vector art then image style transfer could be good for that. Unfortunately I dont know of any good apps that can do it in a reasonable time so I just use https://deepdreamgenerator.com/. And unfortunately again your a little limited on what you can do there until you get more points which can take a while. If you create an account there and want to get full points give me your account url, make some pics and Ill like them all. You can only do low res at first but you can upsample them using AI (lots of apps for that).
If you go the stable diffusion route then look at img2img and depth maps to get it to look like an original pic, youll still have to experiment a lot with prompts to get it right tho, but if you have a half decent graphics card you can do it offline (I only have a 1060 and its still bearable). The latest Automaric1111 build can do them… GitHub - AUTOMATIC1111/stable-diffusion-webui: Stable Diffusion web UI
Have you tried https://paintbytext.chat/ from earlier? It seems like it supports you uploading your own image, providing a text-based description of what to change (ie: give it a vector look), and seeing the edited image.
Would you be willing to share your source image and a few links to the style you want it to be in? One problem here is Im not totally sure what style you want. There are vector images that look like photos, some are more of a colour reduction look and then theres the more polygon look. If you can give me those things it would help to find the best solution for you as theres many different ways to get those looks and AI might not be even needed (I like doing graphic stuff and know a few techniques). Id be happy to spend some time on Sunday (maybe before, but that day for sure) trying a few things if you can supply those images. Oh and what resolution you want it to be.
I know your gone and dont care ;p but for completeness I just wanted to point out that the abilities of paintbytext.chat are now baked into Automatics GUI for stable diffusion. Really got to update my install and try some of the new stuff, just gotta hope my 6gig vram is enough.