Yes. During the COVID emergency, the time people have to elect COBRA is extended by up to one year. So if you lost your job last summer and were then eligible for COBRA, you still have time to elect it.
Normally, when you elect COBRA, coverage applies retroactively back to your qualifying event and you must pay premiums back to that date. However, if you are eligible for the COBRA premium subsidy and if your layoff happened before the new law passed, your COBRA coverage will take effect on April 1, 2021, and the premium subsidy will also start then.
Your 18-months of COBRA eligibility will still be based on the date of your qualifying event. So, for example, if your qualifying event was June 1, 2020, your 18 months of COBRA eligibility will run out at the end of November 2021 (though the COBRA subsidy ends by September 30, 2021.)