An iMac from 2019 can come configured with an Single SSD Drive
It can also come configured with a Fusion Drive
A Fusion configuration can have a 128 GB SSD Drive combined with a Traditional Rotational Drive which usually has a Larger Drive Capacity.
By the magic of Apple, the Fusion Drive is Fused together and presented to the Operating System ( and the user - you ) as a Single Drive
Usually, the Applications are located on the SSD portion of the Fusion Drive as the SSD Drive is much faster
Files like Music, Video, Photos, etc and application files created by the user are normally stored on the Rotational Drive
Which, normal has a much Greater Storage Capacity
Now, Managing Applications that get installed on this computer and occupies space on the SSD Drive.
That falls completely on the User ( you )
Managing a 128 GB SSD Drive will be a challenging at best