It's possible but it's not a wise business idea. If a casino sets 100% RTP, it means that the casino gives back 100% of the money to players. Casinos have lots of expenses and believe me, salaries are very high in casinos because the competition is very high. To sum up, casino has to pay huge salaries to many number of people, as they employ UI/UX designers, front-end developers, back-end developers, IT technicians, cyber security experts, product owners, marketers and etc. Then they have to pay lots of money to these people and they also have to pay lots of money to have a good service infrastructure and have good backups.

Casinos can only set 100% RTP for a limited time, as a promotion. It can't be their business model.