Perhaps try making a simple web chat application. I recommend it for a myriad of reasons:

• You'll get to touch upon all the layers of a web app (DB/backend/frontend) in a manageably small way.
• You'll be able to make multiple choices to learn different technologies - like which database type to use (SQL/document), which message passing method to use (requests/sockets), which frontend framework to use (Solid/Svelte/HTMX/etc), and so on.
• Getting a minimum working system is very fast. You can easily spend less than a day completing this, even as a novice.
• Once completed, there are many extra goals you can set yourself. Try adding roles, commands, enable sending pictures, embedding metadata for links, etc. You need only look to your favourite chat app for your next idea!