yes if you dont have the updated ECUflash definitions then there's a chance it won't be able to read/write the rom proplery.
Your ROM ID is AE5L500V - you can download the very latest ECUflash defs from TD-D's github:
https://github.com/TD-D/SubaruDefs/tree/Alphahit the green "code" button then "download as zip". Take the subaru standard folder from the zip and drop the contents into your "rommetadata" folder in ECUflash.
Once that's done then if you open the rom you should see all the tables and be able to flash changes to the ecu.
You said in the first post that the definitions weren't found in ecuflash now you're saying it's not going into flash mode, so I'm guessing you tried to make a definition for the rom in ECUflash but it's possible you haven't selected the right flash method - updating the ECUflash defs from the github repo should fix that. If there's still no joy then you're going to have to take some screenshots or copy out the text from the ecuflash log window might help give some insights.