Yeah but the question was if I can just but 2133mhz and use it, or only up to 2000mhz and then oc to 2133
I wouldn't even bother upgrading past 1600, because the vast majority of games on older systems gain no benefit from faster ram except in loading levels. Games like Fallout 4 and Battlefield 5 do gain higher or more consistent fps with faster ram, but the results vary more on DDR3 compared to DDR4. What games are you playing right now?
If you are in the US, the cost of a new DDR3 2133 2x8GB kit is as much as a DDR4 3200 kit at $70-90 or nearly 1/3 the cost of upgrading to a Ryzen 5 1600 AF. A used 2133-2400 kit can be as low as $45, but I would save that money and put it toward a full upgrade.
You could upgrade to a R5 1600AF, B450 motherboard and DDR4 3200 2x8GB for around $225-250. The Ryzen 5 1600 AF at $85 is rebranded and slightly slower Ryzen 5 2600. This would give you an upgrade path to Ryzen 4000 8-12 core CPUs.