Powering an ESP32-DevKit with 3 AA batteries
The current i need while the device is fully engaged is around 118mA peak.

Are you using BLE or WiFi? With WiFi it's almost certainly impossible that you're peaking only at 118mA with all the other stuff. Also you need to account for surges. ESP32 on its own for some reason sometimes can spike up all the way to around 250mA. Especially if it's calibrating WiFi power for the first time. You should be mindful of that in your design.

use an LDO-regulator to step down the 4.5V to 3.3V and power the whole system with that.

Since you're using batteries you need to be very mindful of the regulator's quiescent current. For example, the AMS1117 has a typical quiescent current of 5mA. In other words, if you just hook up the batteries to the regulator and nothing else, your batteries would be dead in less than two weeks. You can find regulators that have far less (in uA) like the MCP1700 for example. However such regulators in my experience rarely deliver higher currents. MCP1700 can deliver a max of 250mA and you usually don't want to be living on the edge with this stuff. Keep a large buffer between what your max is and what the chip's max is. Also you need to really study the response graphs of the regulator to make sure it fits your application otherwise you'll have an unstable voltage and the ESP32 brownout detector will keep firing off. You could disable it of course but that's a bad idea.

Does a good boost regulator for 4.5V to 5V even exist

I (being only a hobbyist) would not put any kind of inductors or coils close to my radio. I don't want to deal with any potential EMI issues. But hey that could be only because I'm not a pro/EE.

Is there a 3.3V powered SD-card? This would cut down the problem immediately

There are but that doesn't mean much for your particular project since you're using Vin=4.5V that keeps decaying as the batteries lose charge. For example take this board: https://www.amazon.com/dp/B07PFDFPPC/ If you look closely it uses an AMS1117 regulator. AMS1117 has 1V dropout. This means you're cutting it way too close. Remember batteries are not perfect. Your AAA batteries start at around 1.6V and continually go down. Your SD card can become unstable or flat out stop working as soon as your batteries start to wear out.

Is 5V even enough for the ESP32's VIN pin?

It depends what board you're using. Look for the regulator on the board, then look up the datasheet for that and then you'll know. There is a very high probability that the regulator on your board is an AMS1117 which has dropout voltage of 1V (ie. you need Vin &gt; 4.3V) and a max Vin of 15V.

I read that it can take 12V max, but 10V is more efficient than less than that.

I'm not sure what you mean by that. Could you restate? But in any case, with linear regulators the closer your Vin is to Vout the more efficient. Getting 3.3V out of 12V wastes much more than getting 3.3V from 4.5V. (you can calculate the actual power burned off by the regulator)
Finally I would recommend using larger batteries eg. good 18650 battery. Maybe two in parallel and a discharge monitor.