How do you keep a rollator walker (4 wheels), from sliding across ceramic tile & hardwood floors?

Have patience my friends!
I understand your frustrations because I am now an oldie with a walker!
So often, our children who have grown up with us as their parents, "being the boss and know-it-alls", have a very difficult time understanding that we seniors now need as much help as a young child.
Don't assume we will know after being told once...show us, test us, make us demonstrate that we know how, that we understand what you told us. Don't mince words...use the Nike moto - JUST DO IT! (in a loud voice preferably).
After months of using a "roller walker", I have often forgotten to put on the brakes, something we should do every time we stop...that includes in the grocery store!
Every time my son accompanies me on an outing, he quietly says "Put on the brakes"....and I mean Every Time! It took several repetitions before it sunk in!
It is so important that each of you stop thinking that you are being disrespectful or condescending...JUST DO IT also applies to you.

If you are resistant to the idea of the basic walker there are reverse brake rollators where the wheels are locked unless you squeeze the handle (rather than the opposite as is usual). Try googling
U Step 2 Walking Stabilizer with Reverse Braking System

Might want to switch to a standard walker. Wheels in back posts in front. My mom had several falls with her rollator. I wished I had changed it sooner. She couldn’t set the brakes and it would roll away. Elders have to have decent cognitive abilities to use rollators.

Make me the third to recommend a standard walker. I could never figure out why anyone would use an "old fashioned" 2 wheel walker (or one with no wheels) until my mom needed one, now I know that beyond being easier to control they are smaller, lighter, easier to fold up and bring with you, and they fit into smaller spaces and around furniture much more easily.

Standard walker with tennis ball feet is what my dad used for outpatient PT.

A regular walker with only two wheels would be safer.

There are other types of walkers too. A UStep-2 keeps the brakes on u less you depress them to make it roll. It has 7 small wheels on it and is more stable. It’s designed for people with Parkinson’s, but can be used for anyone. Check it out online- they show a video of it. Dad’s Dr. sent the insurance company a Rx for it and we got a very healthy discount. This kept Dad from rolling away; however, once Alz. got bad he’d simply let it sit & try to walk away. Thought he didn’t need it. Then a wheelchair became necessary.

He needs a walker with no wheels or just 2 wheels and on the legs of them put tennis balls to make the walker slide across the tile easier but won't get away from. Him like the wheels

I would suggest getting an walking aid that's a little less spiffy. Try a two-wheel walker.

I think if you ask pretty much any physical therapist, they don't like the rollator walkers for that very reason. Go back to the old fashioned walker with tennis balls or skis on the legs.