The answer depends on the type of ISA. You may open and contribute to multiple ISAs in the same tax year, as long as they are different types of ISAs. There are six main types of ISAs: Stocks and Shares ISA, Cash ISA, Lifetime ISA, Help to Buy ISA, Innovative Finance ISA, and Junior ISAs (for your children under 18).
That said, you may only contribute to one Stocks and Shares ISA per tax year. You may have multiple Stocks and Shares ISAs each from different tax years, but you must make sure only to contribute to one. You may only have one ISA with ikigai.
Regardless of the type or number of ISAs, your contributions to your ISA(s) in a tax year must not exceed the ISA allowance for that tax year (£20,000 for 2021-2022, excluding Junior ISAs).