Every casino game carries a house edge, which means the expected return on staked money is negative over time. That is the product working as designed. It is not variance, not a cold streak and not something a system corrects.
Holding that clearly in mind is one of the more effective protections available, because most serious harm begins with a belief that losses can be won back given the right approach or enough time.
Sessions running longer than planned. Stakes rising after losses rather than after wins. Money intended for something else going in. Concealing the amount of time or money involved. Irritability away from the game, and relief rather than pleasure while playing.
One of these deserves a pause. Several together deserve a conversation with someone.
Set deposit limits before a session rather than in the middle of one, while judgement is unimpaired. Most operators offer daily, weekly and monthly caps plus cooling-off periods.
Keep gambling money in a separate place from money with a purpose, and never use credit. When a withdrawal is requested, let it go through - reversal is easy by design, and the balance cancelled at midnight is rarely one anybody was glad to have kept.
Self-exclusion at operator level blocks an account for a set period or permanently. Device-level blockers such as Gamban and BetBlocker cover gambling sites generally, and the two work best together.
The National Problem Gambling Helpline is 1-800-522-4700, free and confidential, by phone or text at any hour. Gamblers Anonymous holds meetings in person and online. The same helpline supports people affected by someone else's gambling, which is not always made obvious.