Most of us will use this to reduce the size to something more manageable
https://xerocho.github.io/svgomg/
That's not going to work for this one however because the "Team", "Champion", "Porsche", and "GT3 Cup" are all images which you've thrown on there, which unfortunately doesn't turn them into vector images so they will not scale as such and take up a bunch of room in your SVG file, and they won't show up in GTS if you managed to upload it. Hand trace them or find SVG versions online to use instead, then throw it into SVGOMG to reduce the size. If it still isn't small enough after that you can break it up into parts and upload those parts, it's a pain but better than nothing.