Yes every menu is open for you to customize with Admin Rights

youtu.be/YIZBs3cDB-k

thanks for that but it doesnt show how to customise the calendar, a customer would like to add in the regarding/about column (same as whats in the agenda tab) into the tasks tab?

From the Sage CRM help online - here is the section on customizing the Calendar Customizing calendar list. (https://help.sagecrm.com/on_premise/en/2025R1/Administration/Content/Administrator/CS_Calendar-CalendarList.htm).  this might also help: (+) How to customize the calendar list - Sage CRM Hints, Tips and Tricks - Sage CRM - Community Hub. 

those links talk about customising the calendar list, im wanting to customise the tasks tab under the calendar tab

It doesn't appear to be something you can do through the interface, trying to go through the files in the background that help build those screens and it doesn't look straight forward 

It doesn't appear to be something you can do through the interface, trying to go through the files in the background that help build those screens and it doesn't look straight forward