This is far from a professional model, but I made it out of necessity. I remixed the 3080 bracket and added a bit more length to allow a 5080 to sit in the P3 while still having radiator fans mounted on the side. I still suggest a bracket to hold it up between the card and the PSU since these things are heavy and sag without one. May look at using these glass cover arm mounted rails to add another GPU bracket for peace of mind in front of radiators in days to come by adding a small piece of wood between the two sets to hold them together/up: https://www.printables.com/model/301391-thermaltake-core-p3-360mm-radiatorfan-mount

Links to things I used:
GPU Bracket: https://www.amazon.com/dp/B0FCMF217J?ref=ppx_yo2ov_dt_b_fed_asin_title

Riser Cable(Mine was Right angle V2, 30cm, a little long but it works): https://www.amazon.com/dp/B0CXJLVJXQ/ref=dp_iou_view_item?ie=UTF8&th=1

M4 Inserts/screws for GPU Riser mount: https://www.amazon.com/dp/B07YSV66Y5?ref_=ppx_hzsearch_conn_dt_b_fed_asin_title_1&th=1
amazon.com/dp/B0CQQQ359H?ref_=ppx_hzsearch_conn_dt_b_fed_asin_title_1

M3 Inserts/screws for blade mount (A little off center/wonky, but card doesn't move):https://www.amazon.com/dp/B08BCRZZS3?ref_=ppx_hzsearch_conn_dt_b_fed_asin_title_2&th=1
https://www.amazon.com/dp/B0FWBCZKFG?ref_=ppx_hzsearch_conn_dt_b_fed_asin_title_1