Hi there,
you can use some CSS:
.gb-button-wrapper .gb-button:hover {
font-weight: 900;
}
BUT you will see this causes reflow as the text expands which is not a particularly nice UX and could result in CLS.
An alternative would be to add a transparent stroke to the text that changes color on hover:
.gb-button-wrapper .gb-button {
-webkit-text-stroke: 1px transparent;
}
.gb-button-wrapper .gb-button:hover {
-webkit-text-stroke: 1px white;
}
You may want to increase the letter-space in the buttons typography settings to make the text a little clearer.