You might want to take a look at Lian Li's anti sag gpu kit. It comes with their O11XL case and I use the kit for builds where the mobo has exposed mounting screws on the right side or middle of the board. The picture off amazon's website shows it supporting the GPU from the middle mounting points of a atx mobo. I like to use the along the right side of the atx mobos if possible. These would be the lower right and the right middle mounting screws.
https://www.amazon.com/dp/B07YKGKZWP/ref=olp-opf-redir?aod=1 This kit does help keep the build looking clean without having to add a stand brace.