So I've tried to use bleach but this isn't coming clean. I know it's been a while since it's really been cleaned. Here's a pic:
I am in the US. I have had luck with Soft Scrub (bleach and mild abrasive in a paste like base), and with Zud (oxalic acid); Bar Keepers Friend is also oxalic acid. Comet is also bleach. Get one of those products and Scotch Brite green scrub pads or something similar. Scrub the stuff in there and leave it there. Let it sit all day before you rinse it off.
Plain bleach is really less than ideal for this for a number of reasons. One it does not cut grease and grime at all. Two it is runny and won't stay on a vertical surface. Three you will breathe a lot of it and hurt your eyes and nose.
I had a great deal of soap scum plus dirty-little-boy foot “schmutz” stuck in the crevices of my textured shower basin that resisted mr. clean magic eraser, comet, bar keepers friend, clr, and straight up rage and frustration fueled scrubbing. I finally got desperate and started looking for anything around the bathroom that might work, or intoxicate my troubles away with fumes at least, when I stumbled upon mouthwash (Scope.)
I poured it on, grabbed my scrub brush and guess what?? It wasn’t dirt and soap and body oil after all! It was plaque! Just kidding. It was all those things but I think the alcohol dissolved the body oils that were binding that crap on the shower. I did still have to scrub a bit, but at least I was seeing results. And, it smelled minty fresh!
Not sure how that would work on a horizontal surface...you might have to mix it with baking soda to make a paste, or, simply use a tooth brush soaked in it and just keep re-wetting. It’s worth a shot!
Btw-I can’t tell from the photo because colors are not represented consistently on different screens but it seems there’s an orangey hue to the dirt...there is a bacteria that grows in tubs/showers/etc that has a pinkish orange hue (like the evil slime in Ghostbusters 2). You might have some of that going on. It’s not harmful in normal healthy people, but for anyone immunosuppressed it can lead to infection. My son (who is prone to infections) got a nasty, very large, very painful abscess in his foot from that bacteria which had to be lanced and drained, poor guy (he was 5). It’s worth the effort to get that stuff OUT of your bathroom.