The content that contains flashing at certain frequencies can cause photosensitive disorder.
Instead of viewing the flashing material, the individuals with photosensitive disorder will be able to fully experience the content if the text alternatives are offered.
Blinking – the switch back and forth between two visual states – can cause a distraction problem. Blinking can be allowed for a short time as long as it stops (or can be stopped). Blinking usually does not occur at speeds of 3 per second or more, but it can. If blinking occurs faster than 3 per second, it would also be considered a flash.
Flashing – a pair of opposing changes in the relative brightness of any point in a colour space, normalized to 0 for darkest black and 1 for lightest white – refers to content that can trigger a seizure (if it is more than 3 per second and large and bright enough). This cannot be allowed even for a second or it could cause a seizure. And turning the flash off is also not an option since the seizure could occur faster than most users could turn it off.
Animation – Some content can include animated motion. An element which moves into place or changes size while appearing is considered to be animated. Some users can experience distraction or nausea from animated content. If the content includes animated motions, it is important to enable interaction that user can prevent that animation while navigating through the content.
Source: (WCAG 2.1)