Thanks for reaching out. As PSD is the default format, that's the reason it moves back to the same settings first.
Did you change any export settings? What was your workflow earlier? Would you mind sharing it with us? Once you are done editing your document, open Save a Copy and select WebP from the options provided in the file format drop-down menu to save your WebP file. WebP is also available under Save As when there is no risk of file overwrite or data loss.