In the US it’s usually not possible to invest in crypto assets through a 401(k) since there are typically limited options for investments (often at most a few dozen choices, even for large employers) , but it is possible to move 401(k) funds to an self-directed IRA and then go into something like Grayscale Bitcoin Trust or invest directly in MicroStrategy or another crypto-related publicly traded company.

I did that when I retired (all-in on crypto there) and the smaller one of my wife’s two IRA’s (she’s still working and has a 401(k) too) is crypto-centric.