Hi.
I installed unity version 2021.2.5f1 and playmaker 1.9.4.f2
If you updated unity make sure that playmaker is also updated.
best way to update is to 1st update all your assets (including playmaker)
then update unity.
then update your assets again.
Also don't update immediately from for example U2018 to U2021.
You should do U2019 then U2020 then U2021