The motivation for this question is the recent US travel ban on foreigners entering the country from Schengen area countries, which is due to expand to include the UK and Ireland on Tuesday, and the general climate of countries being locked down or quarantined.
President Trump's proclamation does not apply to US citizens; the travel restrictions only apply to aliens, with several exceptions such as lawful permanent residents, and spouses of residents & citizens. This exemption is one of the reasons that the measure has come under fire as "ineffective" and "politically motivated".
However, I am reminded of the case of the ISIS bride Shamima Begum, who was stripped of her British citizenship by the Home Secretary in 2019, in order to prevent her return to the UK.
That being said, does international law obligate nations to allow their citizens entry to their own country, or are these provisions specific to the UK and the US, and potentially other countries?