Without doing oil analysis we’re all just guessing.
Ditto on that.
I run group 4 synthetics in my “get to work car” (mostly highway miles) and do 10k to 12k oil changes or 1 year using good synthetic media oil filters. If I use the hydo-cracked synthetic oils like Pennzoil, Valvoline, Quaker State Etc. I change at 7.5k or once a year. My wife’s car rarely gets 5k a year put on it so I go with the cheaper synthetic oils in it. I always use good synthetic media filters as I don’t trust cardboard filters for that long.
Anything below group 4 synthetic oil is really not true synthetic oil but is allowed to be classified as such. Do a web search on group 3 vs group 4 synthetic oils.
I always put MMO in the oil about 2000 miles before my next oil change to flush it out.