Regarding the last few sentences about the speedtest, Fibre doesn’t degrade in a way that you get 30 to 40% line speed. DSL did that, fibre doesn’t.

Speedtests for 10G are complicated and will show low numbers because of all the different TCP parameters and schedulers. Sometimes because peering links of your ISP or the speedtest providers are saturated.

When I had 5Gbs fiber with a UDM I could never get it to speed test close to 5Gbps.

My internet network would would test at theoretical limits with proper iperf2 settings. I tried using public iperf servers but wasn't successful.