Do you get a title screen that looks like the attached screenshot? You should see three different commands.
[R]eturn to the View
[J]ourney onward
[I]nitiate new game.

Hit [R] to go back to the title screen, [J] to continue your game, and [I] to initiate a new game.

Also, if you haven't already, I'd highly suggest you read the documentation...the manual, the lorebooks, the reference cards, and the spellbooks. Back in the day, these games weren't really meant to be played or understood well unless someone read pretty much everything in the box.

Another bit of unsolicited advice...there have been a few control improvements made to the game by fans for fans. I'd recommend choosing one or the other. I don't think you can use both at the same time.

The first is Ultima Patcher. (https://www.pixsoriginadventures.co.uk/category/ultima-patcher/) This can install a few Quality of Life (QoL) improvements, like better music, a fix in a dungeon, the ability to attack diagonally, etc. What's nice about the Ultima Patcher is that it can easily and dynamically install and uninstall each QoL improvement so you can play with what you'd prefer.

The second is xu4 (https://xu4.sourceforge.net/), which is a different engine that you can use to execute the game instead of DOSBox. zip up your ultima4 files into a zip called "ultima.zip" and toss it into your xu4 directory (and the u4upgrad.zip file as well if you want upgraded graphics...that file can be found on the xu4 download page). It's a more comfortable user interface with some customization options as well. It's one of the preferred ways to play the game, although there are a few things (like the ability to attack diagonally) that it doesn't provide, so, some prefer the former, and others prefer the latter.

Enjoy!!!