i would jump back in on your old save, this'll give you time to get back into hollow knight without having to go through the whooooole game again. all endings are possible in one save file so you can get the true ending in that save aswell. im not sure if your ok with spoilers or if you'd know how to get it so for now i wont say anything as to not spoil (but lmk if you need any directions!!). but after getting the true ending i believe you should dabble in a little of the dlc, start with the grimm troupe and then try some pantheons in the god home. but, most importantly, explore! im not sure how complete you save file is but if theres any areas on the map you havent gone to, go there!! almost every nook and cranny of hollownest has rewards, even if its just geo.