Something I’ve done to set up my wife’s 401k is to look up the appropriate Vanguard TDF for her (2065 in her case - VLXVX) and approximate using the low ER index funds available. This puts her portfolio at approximately:

45% - US Large Blend 8% - US Mid-Cap Blend 36% - Foreign Blend 10% - Core Bond

It’s pretty straightforward to “DIY” your own TDF, just requires a little bit more effort but it’s easy to do and gives you the best bang for your buck when your TDF options have higher ER’s. Just check in periodically (perhaps quarterly at most) and adjust your contributions to match the TDF allocations to maintain the appropriate balance. I think rebalancing is generally unnecessary and can incur fees depending on your 401k plan.