I have tons of notifications every morning too. Of course, it's very gratifying. It's also really hard to keep up sometimes.
I try to read something from everyone who claps on my posts. Plus, all my subscriptions to read. I don't always respond on what I read; neither do I expect others to do so. I try to respond to at least one out of every five or so posts on which I'm reciprocating. But, I do a lot of reading as well on titles and topics which interest me – and not all of those titles are on Medium. I think I read the equivalent of around 300 pages a day, all told.
I understand how time consuming it all is. That's why I also understand why other avid readers don't respond on every post. I appreciate the claps. The highlights tell me what in my posts stand out for people.
Supportive responses are little gifts from readers that put a smile in my heart. But, I don't expect them every time someone reads my work., Neither am I offended or let down when they don't leave responses. I hope you'll keep that in mind when you're pressed for time. I won't ever be offended or let down.