Bubble is really powerfull, so unless you have a very specifik need, you are probable best of just having everything here. But that doesn’t mean its not good to learn some new skills!
I think it really depends on the platform. I use amazon (AWS) where you could get a 1 year free RDS mysql database when creating a new account. Its pretty hard to grasp at first because aws (as well as azure and google cloud) has a massive amount of information on their dashboards and hundreds of products to choose from, so it is quite overwhelming.
In the aws universe you would have to learn about lambda first and then api gateway. When you have a general understanding of how to access a lambda function through api gateway you could look into vpc/subnet/routetables/security groups which is the system used for separating public and private “stuff”.
With an understanding of VPC’s, you would then place a RDS mysql instance inside a private subnet, in a vpc and connect to the database with lambda. Then you have all the puzzles
The learning curve is quite steep so its really about taking a couple of steps at a time and not go too deep too fast. If you know some coding already i would recommend AWS CDK as the cdk framework takes care of a lot for you. In general, in the beginning most learning will be done in the browser, but as soon as possible you should transition to manage your infrastructure as code - here it helps to learn Cloudformation, AWS CDK, Serverless framework etc., but dont start there!
For resources, I have spent countless hours on youtube (AWS simplified, Stephane Maarek etc), reddit r/aws, http://forum.serverless.com and on amazons on page where there are many tutorials. For coding in general i like firebase.io (youtube), freecodecamp (web and youtube), Dev Ed (youtube) and programming with mosh (youtube).