Biggest disadvantage of PaaS is that a developer can only use the tools that

PaaS provider makes available. A developer cannot use the full range of

conventional tools.

Some PaaS providers lock in the clients in their platform. This also decreases

the flexibility of clients using PaaS.

https://blog.back4app.com/advantages-and-disadvantages-of-paas/#:~:text=Platform%20maintenance,-If%20an%20application&text=The%20main%20disadvantage%20is%20that,possible%20by%20PaaS%20cloud%20services.