No, your EU, UK, or US mobile plan will almost certainly not offer free roaming in the Democratic Republic of Congo.
International roaming charges in DR Congo are typically very high, often leading to unexpected and expensive bills for calls, texts, and especially data usage. Unlike "roam like at home" policies within the EU, these benefits do not extend to countries outside specific agreements, and DR Congo is not included. Major network providers like Vodacom operate in the country, but using your home SIM on their networks will incur significant per-MB, per-minute, and per-SMS fees.
For travelers arriving at N'djili Airport (FIH) in Kinshasa or elsewhere, an eSIM is a much more cost-effective and convenient way to stay connected with local data rates, allowing you to use navigation, communication apps, and access information without worrying about exorbitant roaming costs.