Your fish seems to have bacterial enteritis, and so does mine. This is what I read.

Bacterial enteritis

Etiology: eating rotten food or overfeeding for a long time, contaminated by bacteria.

Symptoms: sick fish often have swollen abdomen and protruding anus. The fish is in a daze, doesn't eat, stops in the corner of the fish tank, and the feces are white flocs.

Treatment: There are many treatments for enteritis. Oral drugs such as Naco, Yufukang, sulfaguanidine, etc. And topical drugs such as turmeric, furacilin, gentamicin, oxytetracycline, furazolidone, etc. Can be diluted, sprayed or bathed, and can achieve good curative effect.