Requirements:
xmodHack tools(fast DDS converter): https://www.nexusmods.com/skyrimspecialedition/mods/60852
LsLIBTools(to create the pak): https://github.com/Norbyte/lslib/releases (Assets>ExportTool-v1.18.x.zip)
ImprovedUI mod: https://www.nexusmods.com/baldursgate3/mods/366


2D Method:
CHECK THE VIDEO TUTORIAL IT IS EASIER: https://youtu.be/F1zwvrthzRc
1# In "_RESOURCES" folder you will find a png "d20" open it in your photo editing software and make you own dice, and save it.
2# Once you save your newly created dice texture, open it try to clear the number 1 only number 1 needs to be deleted (example pic in "_RESOURCES" called clear.png) then save it as seperate image.
3#open blender file called Main.blend, click the dice, materials, in body change it to the texture that you made first and then in rendered mode you should see it applied
4#run the blender script by clicking the play button top left in the middle
5#change the scene to "second" in the top most bar, click the triangle and apply the second texture you made with the 1 text cleared and go to render>render animation
going back to the folder you should see the image of the triangle make sure the name is exactly "d20_faceCover.png" (no quotes)
6# in folders "single_roll" and "double_2" delete the last frames(images)
7#run 1_generateD20.exe (in folder d20 go inside it and you should see the dices 1 through 20 now )
8#run 2_FoldersToSprites.cmd and wait
9# After you have all 25 sprites, select them, right click, xModHack Tools, convert to DDS, Compressed (BC7).
10#Sort by type inside the folder, select all DDS files, cut them(ctrl+x) and paste in your respective mod folder, i have provided one called AnecCustomDice, in that case go into AnecCustomDice\Public\Game\GUI\Assets\DiceSets\TavDice and paste the images there
THE DDS EXTENSION HAS TO BE CAPITALIZED "d20.dds" SHOULD BE "d20.DDS" VERY IMPORTANT OR YOUR SPRITES WILL BE INVISIBLE 
11# Create the pak using LsLIBTOOLS (pick PAK/LSV Tools, in the create Package section just locate your folder folder here its "" )
12# copy pak to %AppData%\Local\Larian Studios\Baldur's Gate 3\Mods, and you're done.


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3D Method:
CHECK THE VIDEO TUTORIAL IT IS EASIER IT IS LINKED ON NEXUS
1# Open blender apply/import/make the materials you want on top of the dice, make sure numbers object is not hidden and it is renderable (the camera icon)
2# Run the blender script by clicking the play button top left in the middle
3#change the scene to "second" in the top most bar, click the triangle make sure it has the same material you made by checking in rendered view and go to render>render animation
going back to the folder you should see the image of the triangle make sure the name is exactly "d20_faceCover.png" (no quotes)
4# in folders "single_roll" and "double_2" delete the last frames(images)
5#run 1_generateD20.exe (in folder d20 go inside it and you should see the dices 1 through 20 now )
6#run 2_FoldersToSprites.cmd and wait
7# After you have all 25 sprites, select them, right click, xModHack Tools, convert to DDS, Compressed (BC7).
8#Sort by type inside the folder, select all DDS files, cut them(ctrl+x) and paste in your respective mod folder, i have provided one called AnecCustomDice, in that case go into AnecCustomDice\Public\Game\GUI\Assets\DiceSets\TavDice and paste the images there
THE DDS EXTENSION HAS TO BE CAPITALIZED "d20.dds" SHOULD BE "d20.DDS" VERY IMPORTANT OR YOUR SPRITES WILL BE INVISIBLE 
9# Create the pak using LsLIBTOOLS (pick PAK/LSV Tools, in the create Package section just locate your folder folder here its "" )
10# copy pak to %AppData%\Local\Larian Studios\Baldur's Gate 3\Mods, and you're done.