Russia's goal hasn't been to move the lines. Their goal is to grind down Ukrainian army until it collapses. You don't have to take my word for it, this was the assessment of U.S. Lt. Col. Alex Vershinin retired after 20 years of service, including eight years as an armor officer with four combat tours in Iraq and Afghanistan and 12 years working as a modeling and simulations officer in NATO and U.S. Army concept development and experimentation. This assessment is shared by vast majority of military experts:

https://www.russiamatters.org/analysis/whats-ahead-war-ukraine

Russia is still an attacking force, they are still the invaders and they are locked in a slow stalemate with a much smaller force.

That's a simplistic characterization. The reality is that both sides do their share of attacks. For example, if Russia takes a bit of territory then Ukraine is forced to try and take it back. Ukraine has also conducted a huge offensive over the past six months on a far bigger scale than anything Russia's done so far, and if attacking is what nets you a lot of losses then this would be the biggest source of casualties over the course of the war.

I don't really follow Rybar, I haven't found them to be all that reliable. People like Vershinin, Macgregor, Berletic, and Mearsheimer have been consistently decent at explaining what's happening, and what they've been predicting would happen actually aligns with what we're seeing. Telegram channels are simply not comparable to actual experts.

55k deaths with 165k wounded is certainly a plausible number in my opinion. However, even with these numbers, Russia clearly has no problems growing the size of the army. Meanwhile, Ukraine has a much smaller population to draw on, and many people fled the country at the start of the war making the situation worse. The fact that Ukraine keeps expanding the mobilization efforts is a strong indicator of serious losses.

Ukraine has three major problems. First is that it's entirely reliant on the west economically, and support is now dwindling. Second is that Ukraine is also reliant on the west for weapons and ammunition which are running out. Especially problematic given that the west is refocusing it's support to backing Israel's genocide in Palestine. Finally, Ukraine is running out of a trained and motivated soldiers needed to hold the army together. Once the professional core is gone, it can't simply be replaced by people kidnapped off the street and given a few weeks of training.

And yeah, it’s the Russian M.O. to use mass instead of quality.

It's absolutely not their thing, and it's just another piece of western mythology. You should read a bit of actual history of WW2 to see this has no basis in reality.