Hi, after converting to png / jpeg, i see the text merged with background, or it looks blurred/ shadow, why does it happen

i recently started noticing it, since i started sending the final artwork for approval on whatsapp. The text gets merged with the background, or should i say it looks blurred or a slight shadow behind the text, i tried changing the font, colour, but i am not happy with the quality, i think it should do better. can anybody help