Can i use a XT 8000 crank instead of GRX crankset
A single ring is quite easy because there is no front derailleur to worry about.
I assume you have FC-RX810-1, which has 110mm BCD, and uses the same chainrings as FC-RX600-1
Wolf Tooth go to 36t https://www.wolftoothcomponents.com/products/110-bcd-asymmetric-4-bolt-for-shimano-cranks
There are some Chinese 34t chainrings as well
https://www.aliexpress.com/item/4000620134076.html
If you want to swap a XT crank you can but you will need to remove (or replace) your BB and fit 3x 2.5mm spacers  https://si.shimano.com/api/publish/storage/pdf/en/dm/MBFC001/DM-MBFC001-01-ENG.pdf
Then your XT crankset will have slightly (0.23cm) wider chainline and substantially (2cm) wider q-factor