Solved! Go to Solution.
Only available for unlocked, (non carrier branded), S21 devices on stock Samsung CSC code BTU.
Please post a screenshot of your, "Software information page", including the, "Service provider software version", details.
Settings > About phone > Software information >Service provider software version
I can confirm that you are on a Vodafone U.K. carrier branded device with CSC code, VOD.
A discussion about changing your CSC code is not something that is normally allowed on these forums. Check-out the Reddit discussion, here...
Makes sense that Samsung would put a stop to that on behalf of their carrier partners. Try, "xda developers", forum for alternative solutions, (if any)...