I haven't played D2 in a while, and the last time I did it was via battle.net. I don't see an option to link to that account, even though there is a help topic on it. How do I get my characters and progress from my battle.net account into my new Steam/Bungie/everything account? Thanks.
Destiny 2 and BattleNet is no longer a thing. If you didn't transfer your characters and other stuff by December 1st 2020 then you will need to start all over again. See the link below for details.
https://help.bungie.net/hc/en-us/articles/360054862491-PC-Migration-and-Battle-net-Login-Ends-December-1-2020-at-9-AM-PST
This change was fully advertised for one full year through various channels. Sorry, you missed those notices.