I know many interesting cases that people were allowed to enter. It simply depends on the officer her/his mood, your attitude etc.
Exactly. Remember that you have to remain humble at the port of entry with the officer. You CANNOT demand the entry. Smile and ask questions nicely, like that you are glad to be here. I know many people think it's their RIGHT to enter when they have TRV but it is NOT. Officers picks up the tone and honestly, they are going to judge your case on documents and the personality you are presenting at the border. With COVID19, you may have to be extra careful with your social distancing and obeying whatever the signage AND officer says. Be prepared to answer questions politely. Arrogance and demanding your rights will not get you anywhere.
I am sure they will be a bit easy on applicants whose visas were approved before March 18th, because the rules are vague and in the open. Just make sure to carry every document to prove your presence is necessary and you have a quarantine plan of at least 14 days (if you can afford and show additional days, that's a plus).