Use CSS Grid to stack items, and visibility: hidden to hide/show spinner. This approach allows the largest item to size the button, and keeps the button text accessible

Help me, you're my only hope I have a button that should display a loading spinner, usually with a different width than the content. but how do I prevent the button from resizing when it does? - I do not want to set fixed pixel width on all buttons - I need a tailwind or react solution

Are you using position: absolute; to overlap elements? It's almost always better to Use CSS Grid instead!