As it's still up to RNG to drop, each time has a chance for it to drop. There is not a specific 'you will get it after x runs' check.
So, There is no bad loot protection for Vex Mytho. Vault of Glass came out on May 22nd 2021. As far as runs go, only 70 runs would have counted. Well, 3 characters X’s 70 weeks. I heard for a week a few months back that people were able to just do Atheon more than just the 3 characters each week and were able to get the Vex. Only two items have bad loot protection, Eyes of Tomorrow and 1K. Sorry that you have not had one drop for you yet.