Is it normal?

He's probably still recovering. Sleep is good for recovery. Another reason for sleeping a lot is poor sleep at night and/or depression.

Not sure what you mean by "a lot" but when my late husband was nearing the end of his life, he slept anywhere from 18-20 hours a day. And that was for about the last 8 months or so of his life.
What does his doctor say about it? It may be time to bring hospice on board as they can better assist you with any questions you may have.
My husband too had a massive stroke and suffered from seizures afterwards. And I can tell you from first hand experience that seizures will wipe a person out. My husband would sleep for many hours after he would have them.
And just because you bring hospice on board it doesn't mean that your dad will die soon. It will just be extra eyes on him, with a nurse coming once a week to start and aides coming to bathe him a couple times a week. Plus they will supply any needed equipment(hospital bed, oxygen, Hoyer lift etc.)supplies(diapers, pads, cannulas, catheters etc.)and all needed medications all covered 100% under your dads Medicare.
My husband was under hospice care in our home for the last 22 months of his life.
Wishing you and your dad the very best.

It's normal for all elders to nap a lot during the day, especially those who have been through the trauma of a stroke and a 2 month hospitalization! You don't mention his age, but that plays a role in taking cat naps too. I'm sure you have a follow up visit with his PCP here soon? And maybe visiting nurses coming in to check on dad now that he's home. If you have questions or concerns, don't hesitate to contact his PCP by phone or even request a video call.

Best of luck.