WAF and LTM policy - apply to same Visrtual server

You can, but you need to control ASM policy application in your Local Traffic Policy.

When you apply a WAF Policy to a virtual server, it auto-creates a Local Traffic Policy that controls ASM and applies it.

If you create a Local Traffic Policy, you cannot auto-apply the policy to control ASM, so the option is removed.

You need to ensure your Local Traffic Policy contains actions to apply the relevant ASM Policy.