I found that when I migrated from a PC to my first Mac (many years ago now) the easiest method was to move the data I wanted to migrate to an external HD and simply drag and drop to the Mac. One hint on doing that is the following.
Say for example you want to migrate your photos from the PC to the Mac. Once the photos are on the External Hard Disk then drag all the photos (yes all at one time) to the Photos app on the Dock. This will move the phots to the Mac and input them right into the Photos app so you can easily manage them. Another example is if you have a lot of MS Word documents on the PC, move them to the External Hard Disk, then drag and drop to the Word for Mac icon on the Dock.
One thing I recommend that you NOT do is to use Wi-Fi to migrate. If you want to migrate by connecting the two computers together make sure both are connected to your router via Ethernet. Wi-Fi has a long history of simply not working when using Migration Assistant.
Once you have completed the migration then reformat the External Hard Disk (which totally erases it) using Disk Utility (Applications - Utilities - Disk Utility) as APFS and use the drive as your Time Machine backup External Hard Disk. If you are not familiar with Time Machine please click Back up your Mac with Time Machine. NEVER EVER operate any computer without a backup that you know works and set Time Machine to backup daily at a minimum.
If you continue to be stuck, please give AppleCare a call and let them know what you are running into. If you don't have that phone number simply click AppleCare Contact Info to locate it in your country.