I can tell you how to use the built-in UV part later. . If there are small spots, it means that you haven't developed it properly and just use plane projection, then select the line on the model along the line you want to cut, and then it will be smooth. If not, just cut a few more times so that the display will be flatter. After unfolding, just merge the large UVs that can be merged according to your own requirements

The built-in expanded UVs are basically flat projections, which is very convenient and you can adjust the angle if your model is not facing directly. If it's axial, adjust the projection angle and if it doesn't work, just get a UVlayout. It seems to work like this~~~ The professional UV tool directly imports the model you want to divide and cuts directly on the model. It's OK. It's very intuitive. Like the one that comes with it is full of messy lines, but you need to practice more to get started with this software. If you can’t get it right, I think it’s not as fast as using the built-in UV subdivision