I just started a new job. My old withholding amount was 23% and my new amount is 34%. Doesn't this seem too high? My income was $105K and is now $140K.

have you properly prepared and submitted to your new employer form W-4?  does the 34% include state income tax?   even with state w/h it seem high so talk to your employer to find out why.

You don’t provide enough information to answer the question. Are you talking about combined state, federal, Social Security, and Medicare? Or are you talking only about federal?

The IRS has an online calculator to help you fill out your W-4 for federal income tax, but this does not account for state taxes or for Medicare and Social Security.

https://www.irs.gov/individuals/tax-withholding-estimator

If your withholding is too high, any excess would come back to you as part of your tax refund.