Install to SSD failed at partitioning
 

I tried installing KDE Neon and Mint 20 alongside Mint 19. The 120 GB SSD could not be divided into two equal partitions. The old retained 99 GB minimum. And both OS could not go beyond this stage. I tried again and received error warnings and warnings an install could fail or be broken.

On restarting without the install media, Mint 19 would not go beyond accepting the password over and over.

Can this be fixed?

Can you check the SSD size with Gparted?

Keruskerfuerst idea is a good start. You can see what you have just make sure you are on the correct drive.

Some installers will fail if they think some previous partitions(s) have linux. May have to wipe the disk and start over.