When one makes a web application sometimes optimization is necessary to reduce load times / rendering times due to large number of downloads or javascript being rendered.

So one thing I know is that Chrome browser (as well as other browsers) provide a built-in profiler that one can use to inspect various performance issues on the web page.

Are there any resources that teach ways that the performance problems could be solved? For example how to reduce number of DOM redraws or how to parralelise downloads from the web page?

Direct advice is welcome too.

Google & MDN has bunch of useful docs available on that:

https://developers.google.com/web/fundamentals/performance/get-started & other sections.

https://developer.mozilla.org/en-US/docs/Web/Performance

And their dev-tools documentation on performance:

https://developer.chrome.com/docs/devtools/evaluate-performance/

https://developer.mozilla.org/en-US/docs/Tools/Performance

Thank you, this helps.