Lost hard drive space. It’s disappeared
You can not recover 300 GB of free space because the small 104.9 MB EFI partition is between the APFS container and this free space. The command below will remove the EFI partition and add the 104.9 MB to the 300 GB of free space that already exists.

diskutil eraseVolume free none disk1s3


The next command will expand the APFS container to occupy the free space. 

diskutil apfs resizeContainer disk1s2 0


If you still feel the "Macintosh HD" volume (disk2s1) is occupying to much space, you may want to ask a new question to address this problem.