not all files were transferred, now what?

This is one potential risk you avoid (even mac to mac, but above all, PC to mac) by proceeding old fashion:

1) get what you want on an external support (time to pick and choose so you don’t use real estate on your mac with stuff you no longer need or want)

2) copy - perhaps by chunks - to appropriate folders you may wish on your mac, or an external drive if not critical.

By critical, i mean anything you’re working with and for which sitting on internal drive will be optimal (music production projects, video). Usually typical Word, Excel, whichever Office files, will not be “critical”, but if you have room and want to ensure to have it on the internal drive, sure go ahead

Which items did not transfer?? One option is to copy and transfer them with a APFS formatted USB drive (i.e. "sneakernet").