Increase/Decrease Engine RPM

I don’t see any controls for Engine RPMs…

If you mean Prop RPM, it’s under “Power Management” in the Controls menu, then “Propellor”. Multiple options there for controlling RPM

What aircraft are you referring to?

RPM is adjusted by two ways in GA aircraft.

Without a constant speed prop, you use the throttle (black lever) - see 152.
With a constant speed prop - use the prop lever - (blue lever)
If there is no blue prop lever then that aircraft has a FADEC engine control and only a throttle and the RPM is computer controlled based on Load.

Thanks for your response and for the tips!
No specific aircraft that I’ve used so far in FS2020.
While mapping certain keyboard keys, I thought about ones that I used/use in FSX and P3D. Several of the A2A warbirds have RPM levers (and it was easy to just have keys mapped to ‘em) . So I’m just kinda thinkin’ ahead to whenever A2A (re)makes the warbirds for FS2020.

Not totally unrelated, has the key command for full throttle (former F4) been removed altogether?

Sounds like you’re referring to the propeller pitch axis. In piston and turboprop engines with constant-speed propellers, the pitch (blue handle) levers control the angle of attack of the blades, which indirectly affects the RPM.

RPM is also affected by the throttle (black handle) lever.

Note that the pitch levers are only relevant on planes that actually have one. Some planes control the prop pitch via the FADEC system based on throttle position, speed etc and no manual intervention is required.

It’s the other way round. You set the desired prop RPM with the prop RPM lever and the constant speed unit or prop governer maintains the set RPM by varying the blade angle.

Throttle affects RPM only when the prop is out of the governing range.

Btw. the reason why I deleted my above post that this was a weird case of an automatic thread resurrection.