The request... return a simple to understand dashboard showing the basic storage detail, by database, with a percentage of storage used.

dashboarding storage capacity.sql

--
-- Subject: Dashboard the storage capacity, including percentage used
-- Author: Scott Forstie  
-- Date  : February 11, 2022
-- Features Used : This Gist uses asp_info
--
--
-- Capacity numbers are in MB units.
-- https://www.ibm.com/docs/en/i/7.4?topic=services-asp-info-view
--
select RDB_NAME, TOTAL_CAPACITY,
       TOTAL_CAPACITY_AVAILABLE, 
       TOTAL_CAPACITY - TOTAL_CAPACITY_AVAILABLE as storage_used,
       decimal((decimal(TOTAL_CAPACITY - TOTAL_CAPACITY_AVAILABLE, 63,2)) / 
         decimal(TOTAL_CAPACITY, 63,2),5,2) as percent_capacity_used
  from qsys2.asp_info where asp_number = 1 or asp_state = 'AVAILABLE';
 

I'm getting PERCENT_CAPACITY_USED 0.00 with that query. Below seems to work, although I can't quite follow how/why:
select RDB_NAME,
TOTAL_CAPACITY,
TOTAL_CAPACITY_AVAILABLE,
TOTAL_CAPACITY - TOTAL_CAPACITY_AVAILABLE as storage_used,
decimal((decimal(total_capacity - total_capacity_available, 63, 4) /
decimal(total_capacity))
* 100, 5, 2) as percent_capacity_used
from qsys2.asp_info where asp_number = 1 or asp_state = 'AVAILABLE';

My colleague had the same problem. :)
Look under your JDBC configuration and make sure that the divide scale isn't set to zero.

Hmm, indeed it was set to zero but I changed it and reconnected, and still have the same issue!

Did you save the JDBC configuration?
You might have more than one, so also take care to look at the bottom of your Run SQL Scripts window to see which one is currently in use.
Lastly, if your ACS isn't at 1.8.8.0, update it to be current.
I tried changing my precision from 5 to 0 and saw the same thing you noted above.