I followed the link you provided and arrived at the latest version (probably). There were no errors like before, and I was able to successfully create a psk file.
However, it seems that depending on the mesh or texture, it may or may not be possible to convert it. In my case, I was able to convert the mesh data of one character, but not the texture. For another character, I was only able to convert the texture. The things that could not be converted were converted with Fmodel, so there was no problem. I don't know if this is the specification of Umodel and Fmodel, but it seems that they complement each other.
In any case, I was able to achieve my original goal. Thank you to spritvod for your advice despite your busy schedule. I will ask you again if I have any questions, so I hope you will help me out in that case.
