I have a iMac 27’ 2019 with macOS Big Sur can i update to Ventura directly, or update first to Monterey and then ventura

Also if you have any "cleaning", "optimizing", "speed-up", anti-virus or VPN apps on your Mac uninstall them according to the developer's instructions.

If you have problems downloading and installing consider booting into Safe Mode according to How to use safe mode on your Mac and download and install from there.

Note:  if you have a wireless keyboard with rechargeable batteries connect it with its charging cable before booting into Safe Mode.  This makes it act as a wired keyboard as will assure a successful boot into Safe Mode.

You should be able to bypass Monterey and upgrade that iMac directly to Ventura.

Be sure you have a current backup of your data before you attempt the upgrade just in case something goes sideways.