I have recently purchased a 5g cell phone (unlocked). I was wondering whether anyone knows a good source for a European 5g sim that could be used when I visit Germany, France, and the U.K. during an upcoming trip. Thank you
I haven't been able to travel to Germany or France for two years but I am in England. Be aware that 5G is very spotty, and varies considerably between carriers. 4G is much more prevalent but not ubiquitous. I regularly drop down to 3G.
I suggest that rather than going broad stroke by country you look at the coverage maps for different providers in the towns and cities where you will need coverage.
Also be careful about the possibility of roaming charges while using a SIM from an EU country in the UK. I've read that one or more of the UK cellphone companies is now imposing roaming charges when its customers cross the Channel. I don't know whether that is happening in reverse.
Your best option is Google Fi. This enables you to travel freely among those countries without incurring roaming fees. It's very convenient.