Created "Other Current Assets" and chose "Investments - Other" to track an investment account. How to I set the Starting Balance so it appears in "Reconcile"?

Normally when you create an account you can enter the opening balance, but since you already created it you need to do it differently

show a deposit to the other asset account and use owner equity investment as the source account for the deposit

If you are planning on tracking a brokerage account buying and selling stock, QB is not set up for that kind of thing at all, Quicken is better.  Just enter the plus/minus numbers monthly in QB using equity draw/ investment as the source accounts