Random “free font” websites with pop-up ads – they may contain malware (though rare on iOS, the font file could be corrupted).
You can find free Khmer Limon font packages (often containing variants like F1, S1, etc.) on these platforms: khmer limon font free download for ios
Search Google for "Limon S1 Regular.ttf" and open the result from a reputable open-source repository like GitHub or KhmerOS. I cannot host the file here, but the steps above will work with any genuine Limon font file. Random “free font” websites with pop-up ads –