My first ride was on a TW200 on a big grassy area. I was so stiff on the bike I ended up with a heavy duty backache that lasted a couple weeks. That wasn’t discouraging because I knew that would pass. When I started riding daily the first few days were limited to 15 minute sessions. That built up to 2 hours a day with half of that practicing.
There’s a silent partner on the bike that nobody talks about, the human balance system which includes the Vestibular, the Visual and the Somatic Sensory Systems. It’s worth taking some time to learn about those. That system does more than just manage lean angle. It also feels changes in traction (which may also be felt as very slight changes in lean angle). The sooner changes in lean angle and/or traction are felt the easier they are to manage. The balance systems can’t feel the bike very well in the beginning (feel of the bike also declines with any short layoff) and that’s a big part of why newbies feel insecure and unstable. The balance system need months and years to reach it’s potential to feel the motions of the bike. Progress is faster by doing drills and exercises.