Hi following the lead of the instructions below - I also fixed the problem. Here’s what I did for those of you who, like me, need a bit of extra detail.
I went to the file named - and clicked on info - then down the very bottom I clicked on the plus sign and added the B user in and set their permissions to read and right.
Then I ran the code at the link in my terminal - and put in my password. And it was fixed! Thanks!
Link
“I changed the permissions of Obsidian.app/Contents/Resources/Obsidian.icns to 0644, cleared the Mac OS icon cache for the user B using this and the icon is now showing correctly for both users”