I think the best thing is to call your broker and

I think the best thing is to call your broker and have a long chat with them about their insurance coverage for different scenarios. For example, what happens if your account is hacked and the money stolen. E*TRADE for example, provides $500k of insurance and Morgan Stanley (who owns E*TRADE) has an additional $1 billion in insurance (in total) for all of their E*TRADE accounts.

If you don’t like what your broker tells you about their insurance coverage, or you don’t feel comfortable with it, then IMO the best thing might be to spread your $5 million worth of UNVC shares out to different brokerages (e.g. by transferring $500k worth of shares to several different brokerages).

I also hope you’re using complex passwords and two-factor authentication to protect your account at all times. This is especially important, because, if your account is hacked, for example, your broker will look closely at how well YOU protected your account from hackers.