Yup but the issue is Telegram already has two separate groups, normal groups (3-200 users), and supergroups (200-200,000 users). For end-to-end encrypted groups, Threema supports 256 members, Signal 1000, Wire 2000, and Matrix has no upper limit. Surely Telegram could deploy E2EE for normal groups. Nobody assumes groups with more than 200 members are private anyway.