Seagate External Hard Drive locked, can only read not write
Solution 1:
Seagate provides an OEM-version of Paragon's Microsoft NTFS for Mac. The software is availbale at: Paragon Driver for macOS (10.10 and above). Direct link: NTFS_for_Mac
The installer build date is Sep 12, 2019. The installer's info.plist indicates compatibility:
MACOSX_MAX_VERSION 10.15
After downloading and installing it (and probably rebooting your Mac), you should have normal access to the NTFS volume again.
This OEM-version only works for Seagate drives!