managing sub accounts of bank accounts

We are a UK charity and want to setup a designated fund. We already have restricted funds, which are managed using a mixture of donors, projects and classes. Our single bank account - connected to Lloyds - has sub-accounts for each of the restricted funds. This works well. I can see the balances in the sub-accounts but the parent account shows the true bank balance. The only downside is that I can't easily see our general funds - I have subtract the restricted fund balances from the parent account, so I would like to set up another sub-account for "general".

I can create the sub-account and record transactions in it. The problem is setting the opening balance. I've chosen to start the new general sub-account from 01/1/2022. If I give it an opening balance, it affects the balance of the parent account and the bank no longer reconciles. How do I give it a balance that represents our general funds without it affecting the parent?