If a multimillionaire puts their assets into holdings and gets it back after their tenure, then the incentive to corruption still exists because they can still make decisions that affect those assets even indirectly.

Not really if they don’t know what the portfolio is composed of, the only way they could definitely positively affect it is if they make decisions good for the whole of the economy.

That’s what I was actually proposing, the politician would transfer complete holding to someone like vanguard and they would diversify the assets in a reasonable way. The politician would not have control over it or even see what stocks are in the account, but still be able to benefit from the country’s economy.

All the politician could see is the valuation of the holdings in the event they do want to liquidate, but again, they wouldn’t directly choose what is being liquidated (because they don’t know what they have)