NSFW?
If so, You must be registered for see element. is definitely up there. You must be registered for see element. is definitely a top candidate too. You must be registered for see element. is in production but haven't tried it.
Here's a third for the Swordbearer. It's very different from Long Live the Princess but it's the same setting and quality.
It's kinetic though in case you're looking for something more sandboxy.
Edit: After checking date of posts :p Did you enjoy it?
Could it be Ecchi Sensei?
I'm not sure if it fits the collar etc. as it was some time since I touched it.
If it's a more recent game it's definitely something else though as I think that one is abandoned.
I normally wait some time due to all rushed releases and false marketing we've seen these last couple of years. I used to make exceptions for certain studios but learned my lesson.
I can't say I care too much about lesbian content personally, but I tend to avoid games tagged with "female protagonist". Almost without fail it's always submissive, rape and/or other abuse.
I'm not hating on people that appreciate that kind of content, I just feel like it's such a poor setup...
^This mainly.
I like the freedom of when to approach different parts of the game but if it causes bad pacing, force you to grind or guess too much I'll get bored real soon. Like any game, it boils down to how well the creator implements different game mechanics with (good) story progression...