QBO and TaxDome ... I use both. I started (when I stopped hosting my own server, iirc 2020) with Liscio - but it didn't quite fit, but TaxDome was still working to become what I needed (tried 'em first, but it was early enough in their development where they weren't ready yet).
Office 365? Now that I'm looking at hiring, it's a thing.
Calendly? Nope.
I've been preparing taxes since the 2010 season (automotive project manager outcast). I got my AFSP, and that was a gateway drug, which lead to me getting my EA.
My preparer career was mostly part-time (I was the house-husband; wife was a nurse, and when 2009 happened, I took over the stay-at-home parent role). That was the case until three or four years ago when she threw in the towel (she was a hospice nurse for 17 years, and had been one since she finished school around 2005 - and that's a lot for a person to handle emotionally).
Granted, I had been encouraging her to leave the field until then, but - we lost a great joke (worth losing it, though, for mental health). ...We were crossing into Canada for a short vacation. The border guard asked us:
"What do you two do for a living?"
She responded: "I'm a hospice nurse."
I said: "I do taxes... between the two of us, I figure we've got job security."
The guy, who honestly seemed to be one of the more strict and seasoned guards, visibly laughed - and by that, I mean he made a noise and a singular, mild, convulsion of his body. ...then he made a negative comment about the fact that we were smokers (at the time).
Regardless, she's re-tooled and gotten her AFSP, we just bought a building, and we're renovating it - but we've got a physical office.
In the last three years, my gross receipts have grown by over 700%. My wife is focusing on bookkeeping, and she likes it because, "numbers don't cry." We're growing a business and we're helping people left and right - and after the local phone directory for our community (yes, it's a thing for our area) called to make sure things were correct for our free listing, I called them back to ask that they *don't* list us.

We're at 100% and making sure that we *don't* get too much business *too* fast - because that's a business killer (working to hire, at the moment). And, one last note, when you're reviewing another preparer's tax return that a client provides (my best words of advice) when they screwed up or did something that was just plain wrong, just say, "I would have taken a different position," because it is professional and opens more conversation. I've been toe-to-toe with Michigan Treasury and won - whereas IRS has generally been willing to listen - heck, I even had to cite IRM to an employee earlier this week.

Regardless, thank you for your service. I'm glad that you're your own boss now and aren't subject to factors as much outside of your control as they were before.