If the 401k plan forced you to cash out for some reason, you had the option to rollover the money to an IRA, but this would be an "inherited IRA" that is subject to certain rules. Inherited retirement plan funds can never be combined with your own funds as if they were yours.
https://www.forbes.com/sites/jbrewer/2025/01/14/avoid-making-costly-moves-with-a-non-spouse-inherite...
If it is less than 60 days since you got the check, you should be able to open an "inherited IRA" at a bank or broker of your choice and deposit some or all of the money. That would count as a rollover or partial rollover and the rollover portion is tax-free for now, although as I said, you have to follow certain other rules about withdrawing the money and paying tax.
