Is there a free theme in which you can upload videos?
And is there otherwise an easy way to do this yourself if this is not possible (code). Via youtube - I find this very ugly. Thanks for tips
Most free themes have a media section that can be added to pages.
Read the docs , example https://help.shopify.com/en/manual/products/product-media
If you mean allow customers of a store to upload video that is an advanced customization you will either have to research ,hire an expert, or use an app.
Beyond that requires improving your problem statement.