I have always worked full-time, and apart from maternity leaves for 2 DC, never stopped. I'd also built up a good professional career before DC, so was pretty independent without EXDP's (limited) contribution.
Although I am a high earner, the biggest challenge I find with being a sole parent to 2 DC under 6 is logistics being completely down to you. EXDP sees the DC when he feels like it; e.g. he will see them 2 weekends in a row, then not again for 4 weeks. He's really unpredictable, and this means I can't rely on the contact pattern. It's his way of maintaining control over me.
At the moment, one DC is in pre-school and one DC is in reception, at opposite ends of town. It's just about do-able now, as pre-school opens at 7.30am. From September, they'll still be in different schools as DC2 has SEN, so needs a more supportive environment for reception. Breakfast club at DC2's school starts at 8am, and I need to be at my City job an hour away by 9am
I also have a new and unsympathetic boss, whose only focus is work, and to hell with staff well-being.
I'm currently searching everywhere for a more local/30 minutes maximum travel job, but the issue I have is that due to my seniority, these are few and far between, if they exist at all.
Unfortunately I need to stay at this level work wise, as otherwise I wouldn't be able to afford the mortgage on the house I'm buying solo, and we'd have to move out of the area.
Hugs to you OP, the advice I would give is to focus on one thing at a time, and don't try and do everything at once 