The main purpose of this study is to learn more about the safety, side effects, and effectiveness of LOXO-435 by itself or when it is combined with other standard medicines that treat cancer. LOXO-435 may be used to treat cancer of the cells that line the urinary system and other solid tumor cancers that have a change in a particular gene (known as the FGFR3 gene). Participation could last up to 30 months (2.5 years) and possibly longer if the disease does not get worse.