I had the same problem where tab from an older installation in android was still stuck in open tabs page in WIndows opera gx.
From the last solution posted here, I took cues and got a simple procedure to clear this 'super-glued' tab bug. If you have Opera sync working (which is the case when this issue happens) and is fully synced upto this very moment so that if you mess this up, sync could restore your latest settings and data after this deed is completed. No backups, sign out sign in, etc needed. Just get ready to delete the annoying bits.
First of all, I closed Opera GX windows (no need to sign out of sync).
Then I went to %appdata% (Press Win key+R and paste %appdata%). It will take you to Appdata\Roaming. Go to the Opera GX sub-folder inside Opera Software folder.
Optional: Take a copy of this folder as a precautionary backup (for the meticulous peeps).
Delete the folders appearing to store sync data ( I deleted folders having storage, local state, sync data in folder name).
Go back few levels in the Windows explorer and navigate so that you reach %appdata%\Local folder. In there, delete the Opera GX subfolder within Opera Software folder. No backups needed here.
Start Opera GX.