XBox Live status reports all green.
However, Downdetector UK indicates there was a spike in reported problems connecting to XBox Live from the UK.
Again, there are multiple pieces that all need to work together to deliver a Software-as-a-Service application like MSFS. It could be a problem at your ISP or the pipe between the ISP and XBox.
Just for future reference, you can always use a Command Prompt to run Tracert to see your connection to Xboxlive.com .
Generally it’s one hop between you and Xboxlive.com , as the servers are hosted in a load-sharing arrangement that’s not transparent to the end user.
It could be your ISP, or in between the routing from your ISP to the nearest XBox load balancer.