Hollow Knight: Silksong

A general strategy that I used in HK and have repeated with SilkSong when I couldn't defeat an enemy is first going into the fight with the only goal being survival. Learn their patterns, figure out how to dodge and avoid their attacks and don't yet attempt to deal damage yourself. That way you'll get a feel for their telegraphs and their reach, and you'll build up some muscle memory for evading.

This boss specifically is a lot easier when you have the dash (sprint).
The main problem IMO is when it corners you. Depending on its attack you can either try to run through underneath it, or do a quick pogo+dash over its head.
If cornered on the left side (where there's less vertical space) I have had some success with simply edging ever closer to the exit - the boss usually does the digging teleport at some point, allowing you to escape.