You should be able to move the chair, but otherwise it should not block being able to select the hatch. Did you try zooming in or rotating the camera? Hit Alt, or toggle World Tooltips on in the controller UI, to see if that helps.
Did you try attacking the chair? A hit or two should destroy it.
There are things that can be done first, but I don't think there is anything essential that must be done before being able to get down the hatch. I'll double check in an early Reaper's Coast save and edit this... EDIT: yes, that works fine straight off the Lady Vengeance. This time I tried the non-violent approach (neither of the initial persuasion options are possible), and when dialogue was no longer useful, got Glenna Graeme's attention with a fireball (a destroyed chair shouldn't block the hatch).
If that doesn't help and you are playing on PC, please email supportdos2@larian.com with your save there (or a Dropbox or Google drive link, etc). If you are using any non-Larian mods, also include a list of those enabled and/or the modsettings.lsx file from your profile folder.
Each save is a folder in the '..\Documents\Larian Studios\Divinity Original Sin 2 Definitive Edition\PlayerProfiles\<ProfileName>\Savegames\Story' folder.
In Windows Explorer you can zip a file or folder by right clicking on it/them and selecting 'Send To | Compressed (zipped) Folder' (and similarly in OSX/Finder).
PS4 saves can be sent, as well, but they would need to be transferred to a USB flash drive first.
In the Saved Data in System Storage section of the Settings menu, click Copy to USB Storage Device, select the relevant save(s) and Copy. From there you can zip the files, then copy to email or upload somewhere and provide a link.
Last edited by Raze; 25/08/20 02:58 AM. Reason: update