How do I know if my 14-30 outlet is able to supply 30 amps or 32 amps?

The maximum rated amperage of a 14-30 outlet is 30 amps. For safety/code reasons, EVSEs follow a 125% rule. This means that a 32 amp EVSE (like the one that came with your EUV) should be plugged into a minimum of a 40 amp circuit.

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If all 14-30 outlets only supply 30 amps, then what good is having a 14-30 to 14-50 adapter to use for EV charging?

You can buy all kinds of unsafe/uncertified electrical adapters on Amazon, there really isn't any regulation around it. The adapter you purchased is meant for RV usage. If you think about the electrical draw that an RV has, its really varied based on what you have turned on in the RV at any given time (heat/ac/lights, etc).

An EVSE is considered a continuous load. It pulls the same amount the entire time it's in use.

If you want to go the route of using your dryer outlet, look at picking up an EVSE like this one https://store.clippercreek.com/lcs-30-24-amp-ev-charging-station and pair it with a device like this https://www.amazon.com/Splitvolt-Amp-Splitter-Switch-Thousands/dp/B0B5FCHDBX/?th=1