Does anyone know how long you have to be actively working before your surgery date to still have everything covered?

I vaguely remember reading something about when you quit, you still have your insurance for like 30 days after or until the end of the month, and then there was something about COBRA and that not qualifying for the supplemental plan (which is how I'm getting surgery)?

I have been struggling a lot recently with more call-outs these past 2 weeks than in my whole time here and I'm really just trying to get through to my surgery date, it's in a month. Thanks for any and all help 🙏