Lossless preserves the decoded audio data. It does not guarantee an obvious audible upgrade. Whether you notice a difference from a good lossy version depends on the recording, codec, playback conditions and listener.
Lossless and hi-res are different things
A CD-quality FLAC or ALAC file can be lossless. A higher sample rate or bit depth is a separate property. You do not need a 192 kHz file for music to qualify as lossless.
Apple’s current guidance says an iPhone or iPad needs an external DAC for playback above 48 kHz. That is a compatibility requirement, not a promise of better sound. Check Apple’s lossless playback requirements.
The label does not fix the rest of the chain
A poor ear-tip seal still loses bass. A harsh recording stays harsh. EQ clipping stays distorted. Fix those problems before assuming a bigger file will solve them.
For wireless playback, check the actual codec and the complete source-to-receiver connection. A lossless source file alone does not prove that the transmission is lossless.
Make the comparison fair
Use the same master, the same volume and the same sound-processing settings. Different album releases or loudness settings can create a much larger difference than the file format. If possible, have someone switch versions without telling you which is playing.
Lossless is a useful choice when storage and data use are not a concern. But if you cannot reliably hear a difference, there is no reason to replace a comfortable IEM you already enjoy.
Related: When a dongle DAC is useful and What a frequency-response graph can tell you.