I had a similar thing a while back and was confused as all heck.....until (eventually...) I realised I still had PhotoShop open, which was gobbling up a chunk of my PC's brain...
@Queen-Eleanor-I other than making sure that you don't have any other resource hungry programs open at the same time.....have you checked that Sea of Thieves and the Xbox app have internet access permissions from any Anti Virus/Firewall you may have? (I went through a period using Panda AV and needed to allow Sea of Thieves permission after every update!!)
Also check they are allowed to run as background apps. (Settings-- Privacy-- Background Apps)
Make doubly sure that only one Microsoft Account is signed into the PC you are trying to play on (signing another one in doesn't necessarily mean the other is signed out! (another thing that had me stuck for a while)
Other than that...make sure Windows and your GPU drivers are up to date.
These may not help but are always worth a try if nothing else is working.
If you are still having issues after trying, your best bet would be to contact Support