When I try to right click a cell in a BUDGET version, adding split is not in the option list, but when I am in the ACTUALS version, I can add a split. Why is this? Here is a screenshot of the Account Details.
The reason that the "add split" option is not available in the planning version is because the account itself is set up as Planned by: Monthly-delta. Because the account is set up as plan by monthly delta, it can't be split in any planned versions since the system will not know how to carryover the data from the actuals version. It will however split in the actuals version since actuals are always planned by balance.
To add splits to the planning version, you will need to update the setting to Planned by: Balance. One thing to keep in mind is that by changing the account setting, the balance from the previous month will no longer carry-over to the next month. If there are specific accounts where the splits are relevant in all versions, another option may be to create sub-accounts instead of using splits.