Start small. If you like having that $100k in cash, by all means keep the $100k in cash.

How much extra cash flow do you have per month? Start investing that bit each month in a total market index fund at a brokerage. You shouldn’t have to worry at all about what happens to that if you have your $100k in cash on hand.

Overtime if you get more comfortable with your risk tolerance, you can always start moving some of that $100k over, if you wanted.

Definitely don’t stop your 401k contributions. That’s money you won’t be touching for another 30 years+ - why worry about it?