Generally the default fund in a decent 401(k) (employer managed but largely employee funded retirement plan) will be a "target date retirement fund" that contains a mix of equities and bonds according to the expected risk tolerance of someone at that age, and generally the equity component is also split between US and foreign equities.
e.g. Fidelity's fund for people planning to retire around 2050 https://fundresearch.fidelity.com/mutual-funds/summary/31579...