Insomnia, slurred speech, memory loss.

My father was taking steroid (betnasol) for around 3years. The first symptoms that we saw was during 2020 lockdown. He started loosing weight and was facing problems of insomnia. Weight loss to be specific was from 85kg to 64kg in 1 year. Further new symptoms like mood swing, aggression were seen. Nextly slurry speech and memory loss were seen. He wasn't able to remember day to day events, couldn't remember some times the names of family members etc. After February he is showing a bit of childish behaviour, mischiefs, use to remember some jokes or comic events from his past and start laughing suddenly. He is having so many negative thoughts regarding many of the family members and other people. What may be the problem?