How does an Update to Monterey from Mojave 10.14.6 effect my Macbook Pro

The only major "problem" that I can think of is that Catalina and later (i.e., Catalina, Big Sur, Monterey) will not run 32-bit apps.

If you have any non-Apple 32-bit apps, they will need to be updated.

See: https://www.macworld.com/article/232735/how-to-check-if-mac-software-is-32-or-64-bit.html

I absolutely concur with @P. Phillips on the dangers of jumping from Mojave to Big Sur or Monterey. Apple assumes people will upgrade to each one in order, but never really tests how skipping a major release will actually work especially when macOS 10.15 Catalina introduced some major under the hood changes which I think the Big Sur & Monterey installers assume have already been made to the existing installation. Our organization has been attempting to upgrade some Mojave systems directly to Big Sur with mixed results. Some systems upgrade just fine, while others fail to the point that we must perform a clean install of macOS since the upgrade completely broke macOS beyond a simple easy fix.

I highly recommend you have a good backup before making any attempt to upgrade macOS. macOS 12.x Monterey has made a lot of major changes yet again beyond the already major changes both Catalina and Big Sur have each made. In fact a lot of people are discovering a lot of things may no longer work with macOS Monterey. Apple has also been making major changes even to the supposedly minor point release patches with macOS Monterey which is sometimes causing compatibility issues for some users (for both third party software and third party hardware).

Definitely make sure all of your third party software and hardware are compatible with the OS you plan to install.

You should always have frequent and regular backups of your computer and all external medial (including the cloud) which contains important & unique data.

The Age of this computer will Govern what newer version of macOS it will Qualify to install. Use About this Mac from the Apple Icon on Desktop - the required Information will be there.

With the above information in-hand - follow this How to get old versions of macOS and verify what version this computer Qualifies to install.  For Best results use Safari to commence the download as Others may not work.

Safari will open a redirect and open the Apple Store where the download can commence.

Computer Qualify for the Monterey upgrade

macOS Big Sur 11 hardware requirements

macOS Catalina 10.15 hardware requirements

Caution - jumping over all the newer versions and directly to Big Sur  / Monterey on Qualifying computers is Technically possible - there are those who have attempted and were successful.

Then there are those who attempted and had less than good results.

Remember, Mojave was released in 2018 and Monterey was released in 2021. There have been some major changes to the Operating Systems since the release of Mojave

If this is a Production or Mission Critical Set-up - a more prudent and measure approach is suggested. 

The above is from observations on the Apple Support Community Forums and IMHO

Tips Big Sir Upgrade Released Nov 2020

Tips Monterey Upgrade  Released Oct 25, 2021

Make Time Machine Backup  is very useful and can be used to Revert to Previous Working macOS

Notation - Mojave is the Last version to support 32 bit applications / extensions and Drivers. Catalina, Big Sur & Monterey supports only 64 bit and there is no workaround.

Suggest using Go64 to find 32 bit application before attempting the upGrade. Some or many of the Application already installed may required update or upGrades to 64 Bit Versions.

Your printer/scanner vendor may not have upgraded the 32-bit device drivers to 64-bit, and thus, offer no drivers for Monterey. Best to check before you leap. Some applications that were compatible with Mojave, may now be subscription, or have an upgrade fee on them, depending on the third-party application vendor.

Check for any Adobe application system requirements for Monterey as what ran on Mojave isn't supported on Monterey without current updates.

Very much concur with @ HWTech.

Especially on the under the hood changes pertaining to Monterey.

In specific case changes between Monterey 12.3 and 12.3.1 and again between 12.3.1 and current release 12.4