You'd expect a lot of same-sex interest among those secret desires, but mostly there are heterosexual longings and battles of the sexes.
The Father (1887): a father-daughter relationship goes wrong.
The Dance of Death (1900): a heterosexual marriage gone wrong.
The Ghost Sonata (1907): A young student discovers that the girl he likes is not what she seems.
By the way, Strindberg is the only writer I know of who is immortalized in two different nude statues, both in Stockholm. The massive, muscular "Titan" by Carl Eldh in Tengerlunden Park.
There are also about a dozen non-nude statues of Strindberg scattered around town.