Security risks of holding a large amount of USDT long-term?

I’m considering holding a significant amount of USDT long term and want to understand the real risks beyond price volatility.

My concerns are:

– Risk of issuer freezing funds

– Exchange account freezes

– Wallet security and self-custody risks

– Smart contract risks depending on the chain

For people experienced with large holdings:

– What are the biggest real-world risks?

– What storage setup would you consider safest?

– Would you diversify across assets or chains?

Looking for serious input from people who’ve handled large sums.