I'm looking into learning MongoDB for a particular job that I think it would be better suited to than our current MariaDB only LAMP stack at my workplace, but I'm not sure which of these would be better to go with.

Their official download page:
https://www.mongodb.com/docs/manual/...odb-on-ubuntu/

or

apt-cache search mongo (if this option, which one of these packages would be best)
mongodb - object/document-oriented database (metapackage)
mongodb-clients - object/document-oriented database (client apps)
mongodb-dev - MongoDB C++ Driver (transitional package)
mongodb-server - object/document-oriented database (managed server package)
mongodb-server-core - object/document-oriented database (server binaries package)

I, and the company I work for also use php a lot and I seen this in the apt-cache search as well:

php8.1-mongodb - MongoDB driver for PHP

If my or my company were to need the mongo/php driver, would we also be able to get/use it if we installed the version from the official site?

Thanks.

they are all answered in the documentation of mongodb. I suggest to start learning there.
Otherwise, the answer depends on your (or your company's) needs.

Seems a bit of an odd question. If it's provided through your online repositories, those would certainly be the ones I'd install, rather than download/compile from source. Updating would be FAR easier. Just typing in "sudo apt install mongodb" gets you what you need, client and server. The PHP extensions are in the other package.

As far as whether it'd be better or not...don't know, since (as pan64 said), it's up to your needs and the needs of the application/company.

Last time I touched MongoDB was migrating a system away from it, to Redis. (Also, a few bits of functionality were reverted to using SQL.)

Otherwise, stick to what's in the repo unless you already have a specific good reason to not do that (which you don't, or you wouldn't be asking).

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Get others at your company involved in the evaluation and decision. Do not make it yourself. You want formal present-state/future-state evaluation as a direct project for one or more teams. Followed by a project plan for the conversion if approved.