Yes, I think seeing a photo or two will help determine why your photos are softer than you would like. There are so many variables that go into getting a sharp photo.
Regarding the cameras, all other things being equal (approx focal length, aperture, shutter, ISO), a full frame camera will give better low light results. As I mentioned in an earlier post, I rented an M6 II and RP specifically to compare low-light IQ, and the RP gave better results. I bought an RP and use it primarily with an RF 35mm F1.8 and EF 85mm F1.8 and the results both indoors and outdoors are spectacular. I do not use flash at all. My Christmas photos which included my running 3-year old were taken in very low light by the Christmas tree.
It did take a while and a lot of experimenting to figure out the best way to set up the camera. On the RP, I almost always use Eye-Detect AF, servo, and continuous shooting. The eye detect on my rental M6 II was good, but it only tracked the eye when the subject's face was fairly large in the frame. My RP tracks the eye with the subject much smaller in the frame, which is helpful. There are also several parameters in the RP's Custom Functions menu that allow you to adjust how Eye-Detect operates and tracks.
Are you shooting RAW and processing in Canon DPP software? That will give the best results and allow a lot of fine tuning of sharpness and noise reduction. My latest set of cameras and DPP default the Sharpening Method to "Unsharp Mask". I've found that Unsharp Mask shows more noise in general than the "Sharpness" setting. I now set all photos to the Sharpness method "Sharpness" with a starting level of 5 and I like the results much better. (See screenshot below):
I can't remember if the M6 II has Digital Lens Optimizer (I'm not referring to the aberration correction, distortion correction, etc., I'm referring to DLO for sharpness which the RP has). DLO works well outdoors, but I actually like the results with it off when I'm indoors.
My general test for indoor low-light shooting is how well I can see individual eyelashes when the photo is viewed at 100%. I'd have to know what you consider acceptably sharp. I'm sure seeing some example photos will be very helpful, along with exposure settings, and autofocus settings.