After playing around with InputFields for a simple text chat prefab, they seem to have many, MANY issues with them. The most jarring so far being that TMP InputFields don't bring up the keyboard unless the "Y" Key is pressed, and said keyboard just doesn't work with them.
Here's a little example just in case, Right is the normal InputField, Left is the TMP InputField
Alternatively, Please allow us to use TMP through the URL InputField > https://feedback.vrchat.com/feature-requests/p/add-tmp-variant-for-vrc-url-input-field