@j4mesj4mes It’s horrible isn’t it!
First I used Bostik Concrete Sealer 5L, really easy, dilute in a bucket of water, then roller it on (I dare say someone would say PVA would do, but whatever). Could have left it at that, it sealed it excellently.
Once set and dry. I Painted with Ronseal Diamond Hard Floor Paint, don’t use that! It is not “diamond hard”. Mine chipped a few times already. But it was the only one available as eveything had sold out due to Covid DIY enthusiasts. Now it’s all done it will be easy for me to paint over it with something else. I’ll probably try the Leyland Heavy Duty Floor Paint
If yours is like mine, single garage with gable roof, I’ve also boarded it out with loft boards. Going a meter out each side from the edge, leaving a clear gap all the way through the middle to get up with a ladder to fetch stuff. Excellent bit of space for boxes of stuff, Christmas decs, body boards etc.