Where to invest ~500 /month

Currently have 1k per wage slave check automatically deducted and put into a credit union savings account through my employer, so 26k per year but that money is just sitting in a savings account and being used as emergency money. My employer has a credit union which is only available to employees but there are no investment opportunities at this CU, just savings and checking accounts. Currently just have a Roth and 401k. No debt other than my mortgage @ 2.5%. I’m going to continue building this savings account but it’s stupid to just have it sitting there and not collecting interest so I want to start putting 500 per month (for now) into an investment account. S&P 500 index fund? VOO? HYS account? What would you do?
My identical twin brother (RIP) was perma'd by teampunishment circa 2012. Miscing in 2023 to carry on his legacy

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