Would this Thunderbolt enclosure give speeds similar to the internal SSD on my M2 mini?

Depends on the speed on the NMVE. Not all are the same. To achieve the 3000 speed requires an NVME rated high like 5000 because external TB drives will be much less than that. The speeds advertised are for internal mounting. I use WD NVME Black drives that achieve the high speeds. Not sure about the Crucial.

I would check ahead with OWC about enclosure/NVME compatibility and if they have tested the drive you desire.

FWIW, enclosure/NVME combinations tend to be very picky and not all combinations are friendly on Macs in terms of performance and reliable connections. This is also not unique to Macs as the issue also appears on PCs. A combo that works amazing on a PC may not work on a Mac and a combo that works amazing on Mac may not work on a PC. There can also be some combinations of enclosures and SSDs that simply just don't work or are unreliable.

Bottomline, you cannot expect to put any SSD, regardless of how high performance it may be, in just any enclosure and expect to get full performance or reliability.

If you look at the description of the enclosure, it is not actually a Thunderbolt enclosure.

It is a USB4 40 Gbps enclosure that is backwards compatible with USB 3, at speeds up to 10 Gbps. Thunderbolt 3 and 4 live on the USB-C connector, and a Thunderbolt 3 or 4 host port is virtually certain to support some form of USB protocol, in addition to Thunderbolt protocol.

Your Mac, like all Apple Silicon Macs, supports USB 40 Gbps mode (which borrows technology from Thunderbolt 3) and should be able to take full advantage of this enclosure. (Provided that you plug it into one of your USB-C ports. If you were to plug it into one of your USB-A ports, with the aid of an adapter, the enclosure might work with it, too – but you would be limited to the much lower 5 Gbps USB 3.0 speed.)

Mac mini (2023) - Technical Specifications - Apple Support

That Crucial M.2 NVMe SSD in that OWC Express 1M2 enclosure would probably be significantly faster than your M2 Mini's 256 GB internal SSD. Whether you would notice the difference in day-to-day use might depend on the application – e.g., are you going to be doing a lot of editing of high-resolution video?

$120 for the enclosure and $50 for the 1 TB M.2 NVMe SSD brings the damage to about $170. You can get a 1 TB Crucial X9 Pro (a preassembled SSD about the size of a credit card) for about half that when it is on a good sale – but that SSD will be more like the 256 GB one in your M2 Mac mini – not close in absolute speed to the one which you're thinking of building.

Crucial specs are fine but you need a TB enclosure to achieve the high W/R speeds. Just be sure the enclosure states that.