Paper from Anna-Sophie Heinze and Marcel Lewandowsky analysed the last German federal elections.
Loneliness (self-reported feelings of being left out, isolated or lacking companionship) are not correlated with populist attitudes, or with far-right voting, at least in this study.
Instead, loneliness correlated with withdrawal from the political process.
This suggests that initiatives that combat loneliness and bring excluded people back in to social circles may not directly reduce the numbers voting for far right parties far right voting, but instead increase overall turnout (which itself might have a diluting effect, depending on how lonely new-voters break down).