sam59, thanks - I will eventually share a proper update once divorce is finalized.
To answer your questions:
1) Yes, I let my STBXW know that I was starting dating as soon as I had made plans to meet with someone in person (more on that below). We were still living together, and she said she had no issues with it, as long as I didn't bring anyone home (obviously impossible) or involve the kids (also obviously a no-no). Interestingly, once she noticed I was having a bit more "luck" than she expected, she expressed surprise and seemed mildly hurt, but nothing crazy. You might think that would be a nice bit of schadenfreude, but if anything I was a bit embarrassed (I know, I know) and tried to downplay it.
2) I don't know her status with the OM except that she has flown out to see him twice this year. I asked once but she didn't want to talk about it, so I stay out of it - none of my business at this point as long as it doesn't affect the kids. And though I still view her as a friend, it doesn't bother me at all anymore, except that I hope she ends up happy.
Legend10, it wasn't much really - I downloaded one of the apps (only one) and it's worked well for me so far. I'd never done online dating, so navigating it took some learning/failing, but I got the hang of it pretty quickly. I definitely wasn't comfortable meeting anyone in person at first (and this was pre-covid vaccines, so it was easy to delay anything under that pretext) so it was all chatting and occasional phone/video calls to start. The video calls were especially nerve-wracking but I felt compelled to go through with them and try my luck.
Once I did move to meet someone in person, I went from complete nerves to almost none - it just took about a dozen in person dates to get there (YMMV of course). It's one thing to say you're not putting any pressure on first dates, but when you truly act on that, it really does take a load off and you can just enjoy getting to know other people, and (gasp) be yourself. Getting physical also took some adjusting - with one person, we didn't kiss until the fifth date, which is kinda crazy, but again, covid, nerves, etc. And again, repetition has made everything more natural over time, to the point where I don't feel rusty anymore, and my confidence is in a much healthier place, even with the occasional rejection. Easier said than done of course, but it really helps to compartmentalize and recognize that every relationship you have from here on out is distinct from your marriage (and other relationships, natch). Sure, we carry baggage, but continue to give others the benefit of the doubt, continue to trust until you're given legit reasons not to, and you'll be able to move on faster than you thought.
I hope this helps - I know you're so fresh from d-day, and I was still in a complete out-of-body haze at that point, so focus on what needs to be done logistically before jumping into dating, but I obviously also believe you don't need to wait years to sort out all your feelings first either. Good luck and keep us posted!