My Mom who has dementia has become very defiant. She flooded the bathroom twice last week. How do you maintain your composure during this?

Mom can't be left alone to go to the bathroom or a flood will ensue, as you've seen. If her care is more than you can handle, place her in Memory Care Assisted Living or a Skilled Nursing care facility with Medicaid. In home care is another option to give you respite, but is likely more expensive than memory care AL.

I was not able to deal with my mothers myriad of issues including dementia, so she lived in Memory Care Assisted Living and did great with "her girls" and I had a life at the same time. I'd have been totally out of my realm trying to care for, and toilet, her at home. Not to mention getting her hoisted in and out of bed, medicated, showered, entertained, fed 3 hot meals a day and 3 snacks, socialized, etc. I had no experience in such things so I left it to those who did.

Best of luck to you.

As already said, only have her use a bedside commode. That will save on the flooding of the bathroom.
Then start coming up with a plan B for mom, which yes will include perhaps placing her in the appropriate facility.
And don't beat yourself up about losing it with your mom, as ALL of us used to be full-time caregivers or still full-time caregivers have lost it with our loved ones at some point or another. It comes with the territory, so be kind to yourself.
Wishing you peace going forward.

Flooding the bathroom.. Perhaps a portapotty may be part of a solution... No more tissues in the toilet. Just put 1/2 roll of paper in there at a time...Save an empty roll and transfer part of a new roll on empty roll...
Poor thing... both of you... I am sorry...

It's not going to be easy, and you will feel guilt when you place her.. Start looking now, and talk to as many facilities as you can, and if you like on or the staff, keep popping in to get another look.. Look to see if anyone is in the main hall, or if everyone is tucked away out of sight... Get your own feel of the places you visit... How do they treat you when you come in? Visually look around, smell, see who is present, approachable, etc...
How do you deal with your LO’s behavior if your a full time Caregiving? I’m at a loss🥲.... See, if you place her,,, your role will be to give her joy, music, milkshakes, fun times, attend activities, etc... :) Leave the care taking to the staff, you enjoy your mom for whom she is. Other family members around? Make weekend picnics or visits... Then again... I did this before COVID... things have changed in some facilities... i keep forgetting...
Best look at a 6 pack.. Since it's a smaller place with less people, restrictions may not be so implemented.

Well, you need help.. Check Salvation Army in your area. They used to offer Adult Day care.. Not sure if they do anymore.

If you can, tour some AL places in your area that may be close by to you. See if they offer "Aging in Place".. they can be in same facility but according to their needs.. etc... You get it.
You may also want to check out your neighborhood to see any one-story homes with a permanent wheel chair ramp at front door. They may be a 6-pack..6 residents, and full-time staff at least 2 people to take care of their needs. If you do drive by one... see if staff will answer the door. If they do, ask for a business card so you can talk to the management and schedule a tour..
It's just you, Mom, and the Dog.... Can she walk? If you can get her into the car, just go to the strand, park and watch the water.

Time to place Mom.

You start making plans for a future where she is cared for by full-time professionals.

I do like that litttle emoji you used. A face with a tear, yet a smile.
Strong.

Do you want to get it all off your chest? Write it down, in a journal, a letter to yourself? Let some of the anger, frustration, sadness out? Grief?

Happy to make suggestions to lightening your load, how to add help, the who, where etc.

SEEING the full load can be the start.