Having to go to each episode and mark it, even though Stremio trakt integration is supposed to mark it, but it only marks them sometimes, is really annoying. Being able to add shows and mass-mark them would be a huge help.
You can mark whole shows and seasons already. Is that what you are asking?
We have a tutorial for this: How to build your watched history - Support / Tutorials - Trakt Forums
Just go to the show page, and make sure you aren’t on an individual season or episode page. Click “Add to History”.
This sounds like a limitation with the app you’re using. As mentioned, Trakt itself allows marking the show or season and watched.