Hi Remy,
Thank you for contacting Syncfusion support.
We have checked your reported requirement and we suspect that you need to select only the unlocked cells only from the locked range (Protected sheet) in the spreadsheet. If, yes we have already considered this as an improvement in our end. For more details, please refer the below link.
Could you please check the above details and get back to us, if you need any further assistance on this.
Regards,
Sangeetha M