If you have CGNAT, the port forwarding on your home modem cannot deliver the connection from the provider's upper network to you on its own. First check your modem's WAN address.
Step by step
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Compare the WAN IPv4 on the modem management screen with the IPv4 visible from the internet. If the WAN address is in the
100.64.0.0/10range, it is a strong sign for CGNAT. -
If the WAN address is a private network address, also check if there is a second modem on top. With the second modem, the provider CGNAT is not managed as the same problem.
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For a public server, request public IPv4 from the provider or use tunneling or hosting compatible with the gaming protocol. If you are going to create a private network with a group of friends, all players must be able to access that network.
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Try the new address with a real Minecraft client from an external network. If you're using tunneling, also check for Java TCP or Bedrock UDP support.
Keep in mind
Just adding a DNS record does not create an inward connection path under CGNAT.