Best computer specs for Premiere Pro to work without any issues

Hello,

I'm curious to hear your opinions on what computer specs work best with Premiere Pro. Here's my short story:

I bought a new 2020 iMac 27" back in September with 3.6GHz 10-core i9 Intel, 128GB RAM, 1TB storage, and AMD Radeon Pro 5700 XT 16GB. I have recently been having tons of trouble working in Premiere and lucky to get 2 minutes worth of work before the app freezes and crashes the computer. Apple Store had it for a few days, downgraded me back to Catalina OS and it's still giving me trouble. And of course this happened with a new client's project that wants it done at the end of this week. Because why not?

So, I decided to go out and buy a Dell XPS 17 from Best Buy. This laptop has an i7 Intel, 16GB RAM, 1TB storage, and NVIDIA GeForce RTX 2060 6GB. This setup is working per se but it's struggling on the export file (20 minute sequence).

My questions are:

How is my iMac giving me trouble being that it's a very powerful system?

What's different with the Dell (other than a windows OS) that seems to be doing okay?

And what system SHOULD I have spent my money on that would not give me all kinds of issues?

Thanks for any input!