I had the same problems on my Mac so I revived an old Windows machine running Windows 7. I was running Magnet - I didn't try to remove it. TWS works fine on the Windows machine. I run one screen on the Windows machine and two on the Mac (plus notebook). The Windows machine is an i7-2600K with 8Gb with a RadeonHD5700 video card.
You can give it a try. Don't need to uninstall Magnet, just need to quit it when you need using TWS. That solved my problem.
Thank you very much for your help! !! I have successfully solved the problem and everything is perfect after I close Magnet!
Just created an account solely to +1 Arthur Wang's solution for quitting Magnet. I thought I had tried everything and that TWS was just a buggy, slow implementation for Macs. Wow - night and day! I'll be submitting a bug report to the Magnet developers. Thank you!!!
I had exactly the same issue with a 2019 16" MBP - top spec, max ram, radeon video card max memory. I was really expecting big things. I had recently installed Magnet for the first time and man was TWS slow AF. I was so confused, especially that it ran like a dream on my 2011 iMac and 2012 MBP...didn't get it. Contacted support, went deep into JVM forums to figure it out . I started running Parallels and running TWS in windows. Then I found this and simply quit magnet, and now TWS runs like a dream. Thank you so much for solving this issue!
Thanks a lot for this tip! I had a similar program called BetterTouchTools to help with my magic mouse and basic window arranging. As suggested by you, I simply quit that program and tried running TWS and it worked like a charm!