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You say that it is possible to get 254 20x losses in a row. And sure, I agree to that. But the probability for getting the losing streak I listed above is much smaller.
It's easy to calculate the probabilty for that (including 1 % house edge) and it is approximately 4.4 x 10^(-13).
Your simulator seems to be able to make around 100 000 tries every second. This means that we can expect the same losing streak to appear once every 43 years in your simulator. I challenge you to try to get it

I'm not sure where did you get your numbers from for that streak calculation
but 4.4 x 10^(-13) is VERY far off
here is what this site shows:
https://dicesites.com/tools 
the probability of 254 losses at 20x multiplier is
0.00025110% i.e. 25%+ for every 100.000 rolls or 100% for every 400.000 rolls (roughly)
you can try and simulate the outcomes here:
https://streakcalc.azurewebsites.net/you will be surprised but I rolled a 252 red streak on my third try:

p.s. not associated with the site in any way,but admin sent me my prize (although with a slight delay due to unforeseen real life issues) and my winnings in full
I don't see how a provably fair site could be manipulating the roll outcomes,if that is what you are suggesting
I checked my rolls and everything seems to be fine,I had a losing streak but that is gambling,things happen
if a more tech savvy admin or dev can look into the site's provably fair system and verifier and confirm everything is in order,will be appreciated