Edit: I found data for more countries, included bulgaria in this edit (a whopping 1200).

Also note that many countries have no purpose built mosques, that is no building that is designated solely for being a mosques. Many have just one or two for their whole Muslim population. Some have no congregation centres for Muslims at all -- for example Slovakia or Croatia (with Hungary heading this way as well).

Kept this to the EU + 2 countries (Switzerland and Norway, who are not members) because there is no actual statistics on this and I had to google everything myself. I also removed countries with less than 100 mosques from the list because they were statistically insignificant. Luxembourg for example has 6, Portugal has 16, Italy has 8 -- by all accounts I could find.

Mosques in Xinjiang: 24'300 in 2013, which is still an accurate number in 2021 according to the CPC. https://www.statista.com/statistics/1085676/china-number-of-mosques-in-xinjiang/

Mosques in Europe:

1. 1500 in the UK https://www.bbc.com/news/uk-35514840
2. 2500 in Germany https://www.dw.com/en/mosques-in-germany-statistics-hard-to-come-by/a-45806004
3. 2200 in France https://www.france24.com/en/20150405-france-double-number-mosques-islam
4. 1000 in Spain https://traveltriangle.com/blog/spanish-mosques/ (sorry for this link, it was impossible to find anything else. Their number is in the Q&A section at the bottom of the page)
5. 100 in Switzerland https://www.swissinfo.ch/eng/mosques-in-switzerland/73624
6. 380 in Belgium https://www.pbs.org/wgbh/pages/frontline/shows/front/map/be.html (dated around 2006 though)
7. 600 in Austria https://www.washingtonpost.com/world/2021/05/29/austria-islam-map/ (and the source is very apropos lol)
8. 170 in Denmark https://www.aa.com.tr/en/europe/mosques-in-denmark-increase-by-48-pct-over-last-decade/1013276
9. no data for Norway
10. around 175 congregations in Sweden. I couldn't find data for mosques specifically, but I found this https://archive.ph/wip/PZNxB
11. 453 in the Netherlands in 2003, doesn't seem this number has changed much https://ec.europa.eu/migrant-integration/librarydoc/the-position-of-muslims-in-the-netherlands-facts-and-figures (see attached pdf)
12. 1200 in Bulgaria https://www.novinite.com/articles/143628/Bulgaria+1st+in+Europe+by+Mosques+Per+Capita

Total number of mosques in Europe: around 10378 (I rounded up the statistically omitted data to 100 for this number)

We could also compare the number of worshippers in both places but I spent enough time on the numbers already so this will be very quick. There are 12 million Uyghurs in Xinjiang and I'll assume they're all Muslim. Meanwhile there are 25 million Muslims in the EU (https://www.bbvaopenmind.com/en/articles/muslims-in-europe-the-construction-of-a-problem/).

This means there are 0.41 mosques per 1000 Muslims in the EU, whereas there are 2 mosques per 1000 Muslims in Xinjiang alone, not even in the whole of China!