Conversations Classic (#637) · Issues · IzzyOnDroid / repo · GitLab
As mentioned in Oct 24th TWIF Conversations Classic was removed due to license violation. The narayana team followed licensing and F-Droid’s inclusion policy properly and now available as another.im.
Reference: The GNU General Public License v3.0 - GNU Project - Free Software Foundation
Especially see the 5th point 5. Conveying Modified Source Versions. and 7. Additional Terms.. Not a licensing expert but as I read the license, credit-to original project in someway is necessary for GPL3. In general it’s always nice give some credit to the original project.
Other reference for quick Attribution details see: ShareAlike compatibility analysis: GPL - Creative Commons