Hello! For some reason, I have 8 greater grove traps. I'm not sure how to access lost grove, is it an event thing? If anyone has any answers, it will be very appreciated. Thank you in advance :)

It's possible they came from the winter advent calendar!

The lost grove becomes accessible once you have finished Astryl's Tranquility (beaten Vorpar) and then gone to the castle in Ethernia and done some dialoguing
The Lost Grove enemies start at lv65 and is very much a spike in difficulty and grind

Thank you for the information, Scathreoite. Does that mean I can't use this pet trap unless I finish the map?

Lost Grove traps can only be used in the Lost Grove, and non-lost grove traps cannot be used in the lost grove, as the two areas have slightly different catching mechanics.
With non-lg pets, what traps you can used are based on pet rarity vs trap rarity, and the wild sylesti can flee, remain, or be caught.
LG mechanics, any trap can be used on any rarity, based on the %hp the target pet has remaining. The sylesti cannot flee the fight, but gets a buff that stacks for each failed attempt making them gradually more dangerous
(Master traps aside; they can be used anywhere because they just bypass all other capture mechanics and autocatch the pet)

Thank you!!