I'm trying to upgrade from Mojave to Big Sur. When I get to the “which hard drive to install” question I select “Macintosh HD” but I get an error saying “This volume is not formatted as APFS”. What the heck does that mean?

It means you were running Mojave on a System File System of HFS Journaled. Catalina and Big Sur can only be installed on the new APFS ( Apple File System ) formatted drives.

One can do the Time Machine Backup ( Mojave ) before going the Big Sur route and Wipe the Internal Drive and re-Format as APFS with the GUID Partition Map - install Big Sur and use Migration Assist during the initial Setup of Big Sur.

The experience of two does not make it the Rule for ALL. Yes, there some with issues, some with issues that do not know how to fix themselves, and those with issues who do know how to fix them. The Double Contacts - do your research and think there is a solution.

dont do it, I updated to big sur and now I have double contacts on my iphone. go figure./.. and no one to help me...

Same thing happened to me with update and now double contacts. Did you ever get it resolved?

No they keep telling me to go to double contacts. but there is no rule for all.....so that was the answer they give me, so if you get an answer, let me know also. but so far, I have no clue..

replying to the group, any ideas group, i actually now have issues with my calendar too.......

if I was computer savy that might work, but since I have no clue what the lingo is, how can I fix it. sorry, but pretty frustrated even more.

read the response they gave me, if you understand it, let me know also...please.