Haven’t read anything by him, but AFAICT he

• was arrested for planning a coup in the USSR during WWII; worth noting that many other countries probably would’ve executed him instead, especially during wartime
• wrote “Gulag Archipelago” based almost entirely on unfounded rumours, and liberals still treat it as gospel (here’s an apparent debunking of his claims, although I haven’t read that yet either)
• was a Russian nationalist and highly antisemitic
• publicly supported Fransisco Franco

I’ve read articles like this but haven’t found any solid evidence yet, so take it with a tablespoon of salt

If you do read any of his stuff, please share your thoughts