exiftool -d %Y "-rights<©$DateTimeOriginal, First Last. All Rights Reserved." -r DIR results in "?2021 First Last. All Rights Reserved."
So © = ? and I can't get it to work, with multiple workarounds attempted.
DNG and JPEGS on Windows 10
See FAQ #18 (https://exiftool.org/faq.html#Q18).
Basically, Windows command line sucks when it comes to non-ascii characters. You can try setting the code page as described in the FAQ, but I never was able to get that to work.
Adding the -L (latin) option (https://exiftool.org/exiftool_pod.html#L--latin) will get a lot of characters to work, such as ©£™ and accented characters, but not if you're using Cyrillic or East Asian text.
Since you're on Windows 10, you can also try this this StackOverflow answer (https://stackoverflow.com/questions/57131654/using-utf-8-encoding-chcp-65001-in-command-prompt-windows-powershell-window/57134096#57134096). This is the only thing that has worked for me, but you may see some oddities elsewhere in other programs.
-L worked for the copyright. Thanks!