Add the font-face rules in the correct order to have the desired result. Smaller font size first, font style normal before italic. Check the example below.
@font-face {
font-family: 'Libre Baskerville';
src: local('☺'), url('../fonts/LibreBaskerville-Regular.ttf') format('truetype');
font-weight: 400;
font-style: normal;
font-display: swap;
}
@font-face {
font-family: 'Libre Baskerville';
src: local('☺'), url('../fonts/LibreBaskerville-Italic.ttf') format('truetype');
font-weight: 400;
font-style: italic;
font-display: swap;
}
@font-face {
font-family: 'Libre Baskerville';
src: local('☺'), url('../fonts/LibreBaskerville-Bold.ttf') format('truetype');
font-weight: 600;
font-style: normal;
font-display: swap;
}