It's difficult because it's easy to miss obscure social niches and name variants, and that's why most people make the task easier with an effort to find unique names.
For example, a sloppy google search for "Rx" yields, in search result order:
- two medical abbreviation, for "recipe" (i.e. "take") in medical prescriptions and for radiography: benign but common and used in proper names of pharmacies, labs etc.;
- Radeon RX-something video cards, unlikely to be confused but likely to yield search result noise for something related to videogames;
- some Lexus cars, popular but more harmless;
- iZotope RX 7, a major software entry: professional "audio repair" DAW plugins from a popular company;
- several unimportant random product and company names, including e.g. some Sony headphones, that collectively prove how "Rx" is an inappropriately short name.
A longer and more unique name would clearly be a better choice. But a further web search for "rx pixel" yields an awful lot of medical video card and car results and a frontal collision on Twitter, where dr. Jennifer Hazel goes by "@Rx_Pixel".
Searching for "rx editor" is also interesting:
- a deluge of iZotope RX results (no hope to become more popular, low-resolution image editors are a smaller niche than audio production)
- the highly popular RxJS JavaScript library. It doesn't take a JavaScript expert to figure out that it's highly popular: the home page mentions a conference about it.
This last conflict should be enough to veto the name "Rx", even without more targeted searches (e.g. social media) and less online-visible usages (e.g. in telecommunications as an abbreviation of receiver or reception, paired with "Tx" for transmitter or transmission).