Glad to hear that Pencil2D is running well for you. Unfortunately tweening is unlikely to happen anytime soon, if at all. The core focus of Pencil2D is on more traditional 2d animation workflows and large changes would be required to add proper object tweening support.
Think of it this way. The things you like about Pencil2D: the stability and ease of use, are both a direct consequence of its narrower focus. Less features means less complexity, making it easier to use and maintain. Pencil2D receives far less development than either Krita or Opentoonz, but they are both trying to do a lot more things at once which is why they struggle with these things.
There are still other programs you can try out if are willing to continue experimenting. We have a list of Pencil2D alternatives you can check out which may have some other programs with tweening support that would work better for you.
P.S. A minor nitpick but freeware typically implies that the software is proprietary but distributed at no cost to the user. Pencil2D would be better described as FOSS (free and open source) or libre.