Any option to run parallelized testing ONLY if the number of tests collected is more than say 20?

For smaller number of tests, setting up 12 workers in 12 cores in my machine is overkill, is there a way to have pytest run xdist/parallel testing only if the number of tests collected is more than 20?

I tried something like below - but it seems the workers spin up before the test collection starts

conftest.py

import pytest


def pytest_addoption(parser):
    parser.addoption(
        "--min-tests-count-for-parallel",
        action="store",
        default=10,
        type=int,
        help="Min number of tests that should be collected before running tests in parallel",
    )


def pytest_configure(config):
    min_tests_count_for_parallel = config.getoption("--min-tests-count-for-parallel")
    config.num_tests_collected = 0
    config.min_tests_count_for_parallel = min_tests_count_for_parallel


def pytest_collection_modifyitems(config, items):
    if len(items) > config.min_tests_count_for_parallel:
        config.option.numprocesses = "auto"
    else:
        config.option.numprocesses = 0


@pytest.hookimpl(tryfirst=True)
def pytest_cmdline_preparse(config, args):
    if "-n" in args:
        args.remove("-n")

The example is in conftest.py; start by tracing when pytest_cmdline_preparse, pytest_configure, and pytest_collection_modifyitems run relative to xdist worker startup. Done means a configurable threshold keeps small collections serial and enables parallel workers only when the collected test count exceeds it.