Is it valid to connect a 5V 74LS241 output to a 3.3V Raspberry Pi input?
This circuit was most likely designed by a non-EE. LS TTL parts have weak high-side drivers so it may marginally work, but NOT recommended. A 74AC241 has strong high-side drivers and would probably damage the RPi.
There are many level-shifters available, you should use one of them.

If you have already built this circuit and the signals are not too fast, you could fix it with a diode and resistor.



simulate this circuit &ndash; Schematic created using CircuitLab