Thanks for the detailed explanation Linas.
Unfortunately it didn't come with any service history, yes I know not an ideal decision and it had 1 owner.
The oil/filter change was done by Halfords as part of an interim check, again probably not an smart idea but at the time I didn't know any local garage.
The paperwork they gave me claims they added 6.3 liters of Xtech synthetic oil and they did not find any issues in the car, the suggested replacing spark plugs and cabin filter following Lexus maintenance schedule, I replaced the filter but haven't replaced the spark plug as it was a bit too complex for me.
My plan is doing oil/filter change at 3000 miles or 6 months as I drive mainly in London and probably you know how the traffic is in here.
I have it booked to be checked on the 4th of Jan to see if I am missing anything as I've now found a what seems to be good independent garage, will see if they suggest adding thicker oil.