Stock recovery won't flash custom ROMs. You need TWRP (Team Win Recovery Project).
The SM-T280 (codename: gtexswifi ) has several solid options depending on your needs: galaxy tab a6 sm-t280 custom rom
Depending on whether you want the latest features or the most stable experience, here are the leading choices: 2021 ROM 7.12 for Samsung Tab A6 T280 LineageOS #Mone Stock recovery won't flash custom ROMs