The Finnish driver will contest a partial campaign in 2022, sharing one of the team's Toyota GR Yaris Rally1 specification cars with eight-time WRC champion Sebastien Ogier.
New for next year is the addition of hybrid systems.
As well as being used for touring stages, drivers will be able to receive an additional boost from the 100 kW hybrid units in-stage.
That, said Lappi, adds another layer of strategy to each rally.
“Using [the hybrid power] is not going to be completely simple,” said the 2017 Rally Finland winner.
“On the test road you understand more where you will use and how you need it, but for the stages you will need to prepare yourself more than before for the stages.
“You need to choose the strategy for the stage and it makes things more challenging in many ways.”
Lappi will open his 2022 campaign at Rally Sweden. Beyond that, Toyota hasn't confirmed his full schedule alongside Ogier.
Initial impressions in testing of the new Yaris relative to the old Yaris, which he took to fourth in this year's Rally Finland, were positive.
“It did feel different after Finland,” he said.
“With the transmission, it's similar to the R5 (Rally2) car and maybe the driving style should be more in that direction.
“Of course there is the extra weight, but also the extra power. It's a rally car, so no problem.
“We were driving a car with lots of different things, many different parts.
“It was more of a development test, let's say. It was very good to be back.”
Elfyn Evans and Kalle Rovanpera will lead Toyota Gazoo Racing's efforts in the 2022 FIA World Rally Championship.