I have 1 TB disk but I'm only seeing 747 GB. How to recover the 253 GB missing?

I am not sure how to solve this. I used to have macOS Monterey on my iMac late 2015 and it was running a bit slow. So I removed it, formatted the drive and did a fresh install of macOS Mojave, which makes it run smooth.

However, the drive is not showing 1 TB in Disk Utility nor Terminal's diskutil list, just the partition with the 743 GB. I am not sure how to regain the missing space.

This is what I see:

As you can see, disk0 shows 1 TB. Anyone knows how to get the full 1 TB back without having to go through the formatting/installation process again?

Thank you very much in advance!