Thank you for posting your question.
In Transifex Web Interface, unfortunately, what you are looking for is not supported.
However, in case you consider the API as an option, you can assign tags to your projects (through project’s settings or API) and then get the details for each project via API including tags as well. That way, you can group them based on tags.
Would that work for you?
More information about this can be found in our documentation guide here.
In case you would like to try our API v3 (preview), you can also check the API endpoint here.
Thank you for sharing your feedback with us.
I will share this with the rest of the team for further evaluation.
Please let me know if you have any additional questions.