@TotallyNotAMeme00 You don't need blindness to hide the player you just need to edit the portal's NBT run this command while looking at the portal /portal set_portal_nbt {doRenderPlayer:0}
Also you can summon fake blocks to give a no-clip effect with this command
/execute align xyz run summon falling_block ~0.5 ~ ~0.5 {BlockState:{Name:"INSERT_BLOCK_ID_HERE"},NoGravity:1,Time:-1000000}
This command will summon a sandblock with a different texture that will never go away unless you kill it . If you want to get rid of it, run this command
/kill @e[type=falling_block,dx=0,dy=0,dz=0]
This will kill the fake block at your position. If you want to get rid of the block 1 or more blocks above your feet, change the dy accordingly
Im also using immersive portals in my version