When Mac IOS Big Sur updated yesterday, my TT 2020 stopped working. I have tried reinstalling twice. After reloading the TT software keeps closing as soon as I open it.

Have you tried clearing your cache? This may help. Help with doing so has been provided for you by clicking here.

I tried clearing my cache's, but this did not help my Turbotax 2020 load.  It still briefly says it is checking to see if it is up to date and then nothing.

@MikeJ50 See this link here for assistance with troubleshooting. If you need further assistance, contact customer support here.