Had a check for you, and can confirm that the BMW Digital Key isn't currently available for the Galaxy Watch. There's more info about the BMW Digital Key availability/device compatibility in the FAQ's here if you want to check it out: https://www.bmw.co.uk/en/topics/owners/bmw-connecteddrive/digital-key.html
Noticed that the Digital Key is available for the S21 series in a few European countries including Uk,France, Germany, Italy and Spain. Imagine that the Galaxy Watch will be supported in due course In the next release it will be possible to pass the key on to five friends. https://www.press.bmwgroup.com/global/article/detail/T0362094EN/bmw-digital-key-now-available-for-an...
I do not work for Samsung or make Samsung Products but provide independent advice and valuable contributions.
My Device- S21 Ultra 5G ( SM-998B/DS ) CSC= BTU , 12GB/256GB
One Ui 4.0,Android 12 Official Version.