You can make your external hard drive to be compatible with both Mac and Windows PC. FAT32 and exFAT are compatible with both macOS and Windows. Besides, you can use third-party software to gain full read and write access to NTFS drives on Mac and APFS drives on Windows.
If you want to use the external hard drive on both macOS and Windows, you should not choose macOS-exclusive file systems such as APFS and HFS+ or a Windows-only file system such as NTFS. When you format the drive on Mac or Windows, you should choose FAT32 or exFAT as the file system.
All versions of Mac, Windows, Linux, gaming consoles, and other devices having a USB interface are compatible with FAT32. On Windows, it doesn't handle files larger than 4GB, and on macOS, it doesn't allow drive partitions bigger than 2TB. Many popular older operating systems are incompatible with exFAT. Because it cannot optimize space consumption for its cluster size configuration, it is not a good alternative for disks smaller than 32GB. Files larger than 4GB can be stored and it supports the largest partition. Now you can choose the one that best suits your situation.
What if you already have an NTFS drive with important files on it and you want to use the drive on Mac? By default, Mac can only read NTFS drives but can't write to them. If you don't want to lose data by reformatting, you can use an NTFS driver for Mac such as iBoysoft NTFS for Mac to fully access the drive without limitation. Similarly, there is APFS for Windows software to let you use APFS drives on Windows.