Two tools that produce STAC items from geotiffs are:
rio-stac is more feature-ful and customizable, stactools is simpler. Here's an example of using and installing rio-stac:
pip install rio-stac rio stac tests/fixtures/dataset_cog.tif
The STAC item will be printed to standard output.
If your geotiffs are from an open geospatial data provider, it might be worth checking https://github.com/stactools-packages/ to see if there's a repository for your dataset already created. stactools-packages can provide richer STAC items and collections that what could be created from the geotiffs alone.