Science

Racial discrimination - depends on the region. Much of Europe is still fairly homogenous, thus the racism there cannot be statistically as harmful as in the US (which is not to say that those areas can't be or aren't quite racist). And yet I don't believe those areas are exempt from the general trend with mental illnesses, as I see at least in my own country. And even in the more heterogenous areas this probably barely begins to account for the trend, the illnesses are not confined to the discriminated populations.

Sexual discrimination is what I include under things that are "at worst, not increasing". If it's not rising , it doesn't explain the rise in mental illnesses.

In the end, out of four proposed causes two are clearly irrelevant, and two can account for the trend only partially at most.

with the rise of right-wing parties

IMO many of these parties are also symptoms of phone and internet overuse too. Much of the ideas, values and language of many new European right-wing parties is clearly imported from online American conservative discourse, without regard for the reality of local society. In my country where gender transitions are very difficult to undergo, where non-binary people simply do not exist in the public sphere at all, new right-wing parties will still talk about the nefarious "gender ideology", declaring there can be only two genders, etc. This is literal Internet-induced delusion.