The easiest path to our manual swap might be to look at the European spec 2019 BMW Z4 2.0i, which will be available with a manual transmission. While that transmission is not a good choice for the Supra since it only comes mated to the four-cylinder engine, and in the U.S. market the Supra is six-cylinder only for now, the surrounding components can be useful.
One of the bigger pieces in doing a manual swap may have already been taken care of by BMW, as the manual version of the Z4 appears to use the
exact same firewall as the Supra. This means that even though the Supra is not available with the manual, all the mounting points for a clutch pedal and clutch master cylinder should already be present. Using the same firewall between cars is not unusual, especially in the case of BMW, as the E46 M3 had provisions for a clutch pedal
even in the SMG version. Since we know that the Z4 clutch pedal and master cylinder will mount to the car, they can be ordered from European BMW dealers once the parts become available to solve that part of the equation.