Would I be eligible for the 2022/23 ISA allowance if I apply for a Cash ISA at the end of the tax year and fund the intended amount after 5th April 2023/2024?

No, the application received near the end of the tax year will only be regarded as opened in that tax year if we have accepted the application before the end of the tax year and your funds are deposited and the subscription is made before the end of the tax year.