I'm afraid there's not so much more that what you are currently doing that can be done, if your goal is that your bike doesn't look dirty.
Fenders are the only mean to prevent the mud from getting there at the first place, having properly fitted fenders with sufficient coverage can improve the situation. While the fender/extension is covered by the question, fender fit doesn't seem to be addressed. I had a look at your questions history and it looks like a suboptimal fender fit may "aggravate" the problem in your case: while your bike (Winora Yucatan Pro?) is fitted with high quality fenders (Curana Apollo), the pictures suggest that they are not optimally dimensionned: your bike is fitted with 27.5" wheels, and the fenders look like they are designed for 29" wheels (and do not cover enough of the front wheel). Having better fitted fenders won't improve dramatically the situation but can definitely be an improvement - especially if they go lower than what you have. Unfortunately, it's very hard properly fitted fenders for 27.5" wheels, especially with wide tires (the only bike I've seen that would match my definition of good fenders with 27.5"in wheels is the 2023 Canyon Pathlite:ON, but Canyon doesn't sell these fenders separately.
A DIY solution can also be to mount "ass savers" as fender extensions, if no extension is proposed by the fender manufacturer, as proposed by GCN.
There's the option to fit protective (hydrophobic) film on the painted parts of the frame, to avoid that the dirt sticks directly on the pain, but that doesn't really help in the context of commuting, as you would need to clean the bike when you arrive at work to avoid that the mud dries. The motor wouldn't be covered as well.