Starting semantic Conventions 1.21.0, many HTTP semantic conventions are deprecated and marked for removal. OpenTelemetry Specification guidelines are to allow opt-into the new and now stable HTTP Semantic Conventionss.

From the specification -

Warning
Existing HTTP instrumentations that are using
v1.20.0 of this document
(or prior):

• SHOULD NOT change the version of the HTTP or networking conventions that they emit
  until the HTTP semantic conventions are marked stable (HTTP stabilization will
  include stabilization of a core set of networking conventions which are also used
  in HTTP instrumentations). Conventions include, but are not limited to, attributes,
  metric and span names, and unit of measure.
• SHOULD introduce an environment variable OTEL_SEMCONV_STABILITY_OPT_IN
  in the existing major version which is a comma-separated list of values.
  The only values defined so far are:
  • http - emit the new, stable HTTP and networking conventions,
    and stop emitting the old experimental HTTP and networking conventions
    that the instrumentation emitted previously.
  • http/dup - emit both the old and the stable HTTP and networking conventions,
    allowing for a seamless transition.
  • The default behavior (in the absence of one of these values) is to continue
    emitting whatever version of the old experimental HTTP and networking conventions
    the instrumentation was emitting previously.
  • Note: http/dup has higher precedence than http in case both values are present
• SHOULD maintain (security patching at a minimum) the existing major version
  for at least six months after it starts emitting both sets of conventions.
• SHOULD drop the environment variable in the next major version.

Mule OpenTelemetry v1.4.0 upgraded Semantic Conventions to 1.23.0 (see #124) and thus now should support emitting stable HTTP semantic convention attributes.