I ran into something similar where the main Syncthing interface was limiting a folder to “Send Only” with that same “locked to read only” message. In my case I was able to work around it by going to the Web GUI and there I was able to set the folder in question to “Send & Receive”. I don’t know if it will apply to your situation, but you might give that a shot if you haven’t already.
It can be enjoyed casually solo or with close family like a girlfriend or teenage kids.
One thing to be aware of is that it’s not designed for drop-in multiplayer. I offered to be player 2 for my girlfriend’s playthrough and now any time she wants to play by herself my character is stuck in her party, not following her around and taking up a slot that can’t be allocated to one of the origin characters.
(UPDATE: This last bit may have been a transient bug; I was able to get the character to follow again after some troubleshooting. Still can’t swap the character for an NPC though.)
So unless you know your other multiplayer buddies can always play with you, think twice about MP or you may be at a disadvantage.
I don’t know how well known it is, but this sort of information is visible already on https://isthereanydeal.com.
Click on a game and look for “Waitlist Price Distribution” under the “Stats” tab: