When an IPO is oversubscribed, the public's desire for shares exceeds the total number of shares issued by the underlying company. A good underwriter will increase the number of shares available and/or raise the IPO's price because the intent is to sell all shares, raising the maximum amount of capital for the company.
Sometimes, the underwriters mildly underprice the issue to facilitate a post IPO pop for some additional buzz. Sometimes, the underwriter(s) get it wrong, severely underpricing the issue. In either case, the underpricing may be exacerbated if after the IPO is set, public interest soars, leading to a large excess of buy orders.
In the case of RLAY, the IPO price was $20. The sharp buy order imbalance before trading opened resulted in an opening price of $35 which is where initial buy/sell equilibrium occurred. After that, price range traded all day and it closed almost at its opening price of $35.