Questions for software developers, designers and project/product managers that have ever needed to estimate software

Hello Software Developers, Designers & Project/Product Managers!

A little bit of background on me. I'm a UX Designer and Front-end developer by trade, now focusing more on leading agile teams to build successful products.

I have a pretty simple couple of questions I'd like to ask in the hope of gaining more insights in the area of software estimations and how teams across the industry are conducting them:

1. Do you estimate software for work or your customers? If so, how often does it happen? (Per iteration, per milestone, per ticket, etc)
2. Who is part of the estimation process? Is it performed through synchronous channels (In-person, zoom, etc)?
3. Does your company have tools or certain methods available to help your development teams estimate?
4. Other than not being accurate, what is your biggest pain point with estimating?

Any response you can provide to the above questions would be greatly appreciated. Thank you and happy to field any further discussion or clarifications below.