Adjust cash balance in investment account.

I assume you have setup your Quicken investment account with a linked Quicken cash account.

First: The "Update cash balance" option for investment accounts is not itself a transaction type: it's a menu choice. It is found in Investing > Investing Activities > Update Cash Balance. Completing that menu choice for an investment account will generate a MiscExp transaction for the account ... which you could do directly without using the Update Cash Balance option.

But ...

Second: You can not use "Update Cash Balance" in a Quicken investment account with a linked cash account, because that investment account can never have a cash balance. Whatever adjusting you do needs to be done in the Quicken linked cash account.

[Technically, you could enter a MiscExp (which would automatically become a MiscExpX) in the investment account. But that would still adjust the cash balance in the linked cash account.]

Can I just put in a misc adjustment directly in the cash account without effecting the investment account?

No offense intended, but I think you are misunderstanding what is happening.

Yes, you can enter a transaction in the linked cash account and it will not "appear" in the investment account. But it will affect the cash balance that Quicken associates to the investment account. Presumably that is what you want to happen; presumably that is what happened in the real world.

Quicken's "linked cash account" was (I believe) intended to handle a situation that was occurring in the real world that Quicken could not, otherwise, have easily handled: namely, writing checks from investment accounts. I think it is a sort of "gimmick" to allow users to enter "checking account type transactions" whose impact would ultimately fall on the associated investment account.

Newer versions of Quicken allow you to write checks, and make other "bank account" type transactions directly in your Quicken investment accounts ... without the need for a "linked cash account". A much better approach, in my opinion.

If that does not describe what happened in your real world, you would need to supply more information.

Thank you. So I guess it would be better to unlink the accounts and then and then debit or credit investment cash events in the cash account as they occure,

I'm not sure why you would need to adjust the cash account, but you can enter an adjustment transaction directly in your linked checking account (without unlinking the accounts); just use the account itself in square brackets as the category. Or put a MiscExpX transaction in the investment account.