Have you gotten a good answer since you posted (3 years ago)?

From what I did (in Odoo Online v18.4e) is to tag accounts that are not "Bank and Cash" type that you think cash will directly flow in or out of. No need to tag "Bank and Cash" type of accounts as they're disregarded (they're the source of the cash flows to begin with).

All cash movements to these accounts will appear in the CFS, categorized under the tagging you made. If you had left out an account that is not tagged, cash flow in/out of it will still be in CFS, but just under "Cash flows from unclassified activities" section. You can fix it by checking and tagging the accounts in Chart of Accounts to what tags they should be in.

About advance payments from customers / to suppliers... This is what I observed (although I can't find a specific documentation to confirm this behavior):

To show a cash flow for "Advance Payments received from customers" in the CFS, the bank or cash deposit (debit) must have a double entry (credit) using "Accounts Receivable" account. I'm not sure if reported is hardcoded to this or it can accept any account of Receivable type.

To show a cash flow for "Advance payments made to suppliers" section, similar approach to above but with bank or cash withdrawal (credit) having double entry (debit) using "Accounts Payable" account (or probably any other Payable type).