Reverse tethering Macbook Pro and iPad over BT extremely slow

Bluetooth is a low data rate protocol and is generally capable of less than 2Mbps under normal circumstances.

Bluetooth 3 supported a "High Speed" mode which used a WiFi link to achieve 24mbit, but is not "real" Bluetooth:

Bluetooth v3.0 + HS provides theoretical data transfer speeds of up to 24 Mbit/s, though not over the Bluetooth link itself. Instead, the Bluetooth link is used for negotiation and establishment, and the high data rate traffic is carried over a colocated 802.11 link.

This requires hardware and software support and generally was not well received or used.

For core Bluetooth support you have the option of 1, 2 or 3 Mbits, depending on implementation and support by both sides of the connection.

Originally, Gaussian frequency-shift keying (GFSK) modulation was the only modulation scheme available. Since the introduction of Bluetooth 2.0+EDR, π/4-DQPSK (differential quadrature phase-shift keying) and 8-DPSK modulation may also be used between compatible devices. Devices functioning with GFSK are said to be operating in basic rate (BR) mode, where an instantaneous bit rate of 1 Mbit/s is possible. The term Enhanced Data Rate (EDR) is used to describe π/4-DPSK and 8-DPSK schemes, each giving 2 and 3 Mbit/s respectively. The combination of these (BR and EDR) modes in Bluetooth radio technology is classified as a BR/EDR radio.

In 2019, Apple published an extension called HDR which supports data rates up to 8Mbit/s.

The 8Mbit extension is unlikely to be common, and would require hardware support. I doubt a simple software upgrade would enable it except on devices that already support it.

It may be that you are thinking of WiFiDirect which is a high speed WiFi connection with a Bluetooth style ad-hoc connection.