Yeah paint removal is probably necessary to get proper bounding of the layers. Maybe there is some kind of primer but that is dependent on the used paint.

For reference I used something the like of this: https://www.amazon.de/PRODIAMANT-Diamant-Schleiftopf-doppelreihig-Diamantschleiftopf-PDX829-025/dp/B00ECWRMRQ/ref=sxin_21_pa_sp_phone_search_thematic_sspa?content-id=amzn1.sym.b3c099a2-7e6a-4a1a-a4ce-a6664d93a79f%3Aamzn1.sym.b3c099a2-7e6a-4a1a-a4ce-a6664d93a79f&crid=31H826ZLPVMNE&cv_ct_cx=scheibe+f%C3%BCr+beton+glatt+schleifen&keywords=scheibe+f%C3%BCr+beton+glatt+schleifen&pd_rd_i=B00ECWRMRQ&pd_rd_r=1f678aa0-59d1-4cff-a672-ab42d2d97de4&pd_rd_w=mqj65&pd_rd_wg=IiuxU&pf_rd_p=b3c099a2-7e6a-4a1a-a4ce-a6664d93a79f&pf_rd_r=7D02EYS1CFND0XQB39S8&qid=1675030594&sprefix=Glatt+scheibe+%2Caps%2C147&sr=1-1-6e6ea531-5af4-4866-af75-1ef299d1c279-spons&sp_csd=d2lkZ2V0TmFtZT1zcF9waG9uZV9zZWFyY2hfdGhlbWF0aWM&psc=1&smid=AHP4NSCWH5R9U

I used an angle grinder with a diamond grinding disk to flatten out an old wall but the concrete parts are tough and take some time.

You could also add a layer of mineral plaster to get a new texture and even out the pattern. Or a combination of both ;)