I'd like to combine 任 as the upper part with 鸟 as the lower part. I was wondering if anyone would be able to help me to find the unicode character for this or help me type it on a mac computer. A guide for typing compound characters would be equally helpful. Thanks!
鵀 is actually an existing character in CJK Unified Ideographs (U+9D40), meaning hoopoe 戴胜鸟. But since it's not frequently used, the corresponding simplified character 𬸊 is in 扩E：2CE0A.
There is an input method called 两分输入法 offered by 字海. The instruction for the input method is here. Basically you type the character by the pinyin of two of its components.
You can directly install the Windows version or install the rime scheme. In the latter case, it can be used across flatforms. You can follow the instructions to install rime on Mac. There is also an online solution where you can type the two components with whatever input method you want and search for the character.