Seeeduino v4.2 not showing up as selectable board in ide

Help! I bought several seeeduino v4.2 and optical encoders with plans to use them in a class. When I follow instructions here

I do not see an option to add my board as an option, so that I can select it in board manager, even though the description shows that I should be seeing it. I do see options for other seeed boards. I am using an ubuntu computer but have the same problem with windows.

Please help. Thanks

Hi @steve_g
For seeeduino V4.2 boards, you should use this URL to add it to Arduino IDE.
Open your Arudino IDE, click on File > Preferences , and copy below url to Additional Boards Manager URLs
https://raw.githubusercontent.com/Seeed-Studio/Seeed_Platform/master/package_legacy_seeeduino_boards_index.json

But for seeeduino V4.2, it is the same as Arduino UNO, you can download the Arduino AVR boards and select Arduino Uno in Tools–>Board.