Hi Jack, congrats on starting your investment journey nice and early.
What you choose to invest in really depends on how interested you are in economics and financial markets. If you’re after a decent return over a long time but have other hobbies that take up your time then passive investing could be the way for you. Here’s a topic where the community has discussed some passive portfolios
If you want to get above average returns then you will need to invest some time to research where the best opportunities are. This is when you start to think about countries, sectors , themes that might see better returns than the average. It took me over 6 months to get to a stage where I felt confident in taking a more active approach in my investments (of course I was genuinely interested in the markets). Until I reached that point I stuck to a simple portfolio which consisted in ETFs that tracked some of the major indexes like the S&P 500, FTSE All World, FTSE 100 etc. Edit: Of which a large chunk is still in passive funds.
Lots of users have asked questions about where to get started so you can read some more topics in