This is a solution for anyone who is interested.
I use VS2019 and standard SQL on my laptop. I have created a small app with a DGV of 300 rows and 270 columns (81,000 cells).
At load I read from a DB table and populate the dgv, and it takes quite a few seconds (no user would pay for this kind of performance, but it's a little thing I do at home)
I have tried to index the table but that did nothing, so I was left with the rendering being the issue.
I sorted it out by making the dgv visible=false at design time.
I then run the program, do the data load to the dgv, and finally, at the very end of the Load sub I make visible=true.
It now populates in less than 2 seconds! A win!!!