Sensible, long-term investing can be the simplest thing to do... you just need to ignore the very many people that want to give you help and advice. They probably have a vested interest. They may well be parasites...
To keep things simple, you can get by with just two investments. A global, passive tracker... and a low risk, short term, high quality government bond fund. You just need to decide on your risk tolerance and investing time frame. Generally, in your 20's, and if you can tolerate fluctuations in your investments, you can be 80-100% in shares, with the rest in low risk, but low return, bonds. As you get older, it's sensible to reduce your exposure to shares, and move them to bonds, in case share investments fall heavily in the year or two before you plan to retire.
Vanguard Lifestyle funds essentially decide the level of risk you need and/or can tolerate. 100/0, 80/20, 60,40, 40,60... that is your split between shares and bonds. Shares are higher risk, higher return. Bonds are lower risk, lower return.
IMHO, these funds are ok. They are fine. They are sensible for many... good for novices, and ok for people who don't want to pay for financial advice. They are not the most efficient, though. They have a home, UK bias. Trust in global capitalism to avoid this.
Nobody cares more about your money than you do. It's worth the investment of your time to learn this stuff.