I recently started this hobby in December. Some RC models are sold with basic transmitters & some of those are RTF (Ready To Fly) models that have transmitters compatible with Spektrum technology. That makes an upgrade easier when you’re ready to upgrade to a 6 channel with model select options. RTF models you already own might work with your upgraded transmitter. Often, the first upgrade for a Spektrum is a DXe transmitter, a mistake in my opinion. The DXe is barely more sophisticated than the simple transmitters that come with RTF models. I bought one RC model aircraft that was not compatible with Spektrum & eventually regretted that purchase, but with upgrades comes other cool gear, like receivers & ESCs (Electronic Speed Controls) that can fix incompatibility. I never intended to get very involved in this hobby. Hahaha. To late now, for me, this hobby is a good friend that’s a time bandit with access to my wallet.
I don’t regret upgrading to a Spektrum DX6e even though it’s not as sophisticated as many other transmitters. It works well for me because it has Blue Tooth buddy box technology. That really matters to me because it saved my models long enough for me to learn something from them. Ask hobby your stores & suppliers if a model you’re interested in is compatible with Spektrum technology, you might find that useful.
Welcome to the forum & good luck flying.