If your Mac has less than 45 GB of free space available on the internal disk, you can setup and run Parallels from an external hard disk.
You'll need to have this external hard disk attached to your Mac while running the Windows-based software, but you can disconnect it when not using Windows.
The key to using this strategy successfully is to get the fastest external drive that you can reasonably afford. Since you'll be accessing the files on this external drive continuously while using Windows, the speed of the drive has a very big impact on the performance of the Windows software.
Here's a link to some USB-C external SSD (solid state) drives on Amazon.
- The key is look for a speedy drive (one that says "up to 1050 MB/s" or "USB 3.2 Gen 2" or faster).
- The size of the drive is up to you and your budget. I'd recommend a 500GB drive (available for around $69) or larger.