Hi,

When I try to enter the Old Sycamore for Lindzi's friends question, I get an error:
"Error: Invalid JavaScript property idenitfier charachert: ,. Path
'm_EntityData[207].Descriptitor.Progression.Features.m_Facts[5].m_Component
sData[0].m_AppliedFacts.$value[1].m_Context.Params.SpellLevel', line 1,
position 3997698.
at Newtonsoft.Json.JsonTextReader.ParseUnquotedProperty () [0x000ef] in
<4f213745d60e425fn763df319c826ddf>:0

Searching found something on the Steam Forum suggesting that it is one of the save files (.json) that became corrupted.
Has anybody else had similar issues? Any idea how to find the correct file and place to fix the SaveFile? Or to know how far back I have to go and replay to miss this error? I went back a few save files, but get the same error when I get there, so I assume I would need to go back to an even older savefile. But how much do I need to replay to miss the error? Or any idea how and which file to fix?

I have got very similar problem, although the error message is a bit different:
Error: Invalid character after parsing property name. Expected ':' but got: e. Path 'm_MainState.m_EntityData[332].UniqueId', line 1, position 5537792. at Newtonsoft.Json.JsonTextReader.ParseProerty () [0x00149] in <4f213745d60e425fb763df319c826ddf>:0

It also permits me to enter the Old Sycamore. I could not solve the Jaethal's quest. It was annoying, but sufferable. But now it is about Linzi!

I am playing Linux GOG 2.1.5d version. Is there any workaround to get to the Sycamore or at least some way to edit the savegame and cheat the quest solution?

No idea about "legit" fixing your savegame (maybe there're some editors), but if you want to cheat your way through bugs you can use mod called Bag of Tricks. It's basically a in-game console with QOL features, but also cheats including quests parameters. So I guess it might help.
https://www.nexusmods.com/pathfinderkingmaker/mods/26

Thank you very much for leaving this here, helped me fix the same exact problem.