Do you really need 2023 MBPro to join WiFi6e

Use Wi-Fi 6E networks with Apple devices - Apple Support

A software update cannot make a hardware radio use frequencies it was not designed to operate on.

Your Mac can use the WiFi, but unless it is in the list of 6e capable Apple products, as specified in the above link, then it will just use the WiFi frequencies it is designed to use.

This is not my area of expertise but based on a few searches, it appears to me that software/apps alone aren't enough. There are hardware requirements as well (i.e., the older Macs don't have the necessary hardware).

As for being an easy fix, that would require openibg the Mac’s case, replacing the Motherboard with a motherboard that has a WiFi 6e capable chip.

Basically replacing the current Mac with one of the supported models, only in your old case.

Apple is not going to do that.

Your MacBook Pro can connect to that LinkSys MX8500 Wi-Fi 6E router, can use WPA3 security, and can operate at full IEEE 802.11ax (Wi-Fi 6 & 6E) speeds.

Just not in the 6 GHz band.

If you’re in an area where 2.4 GHz and 5 GHz bands are overrun, this can be a consideration. Otherwise, I’d be hard pressed to notice the difference between 5 GHz and 6 Ghz. I’m in the midst of rolling a network to 6E, too.

And as usual in recent times, IEEE 802.11be / Wi-Fi 7 is expected to arrive next year; in 2024.