If you’ve truly trusted Christ as your Savior, then going back to calendar rules, feast days, or ceremonial observances as a requirement for being right with God is a spiritual slap in His face no different than keeping them for gratitude, it still serves as a ‘work’

Keeping these or remembering these like it’s a necessity or even just to say “thank you” can create wrong thoughts, beliefs, and responses to Christ and Scripture.
It’s like standing before the cross and saying, “Your blood wasn’t enough; I still need to keep these days to be acceptable to God.” That’s not grace; that’s law wearing a religious mask.
Colossians 2 says those feasts, new moons, and Sabbaths were shadows pointing to Christ; the substance is Him. Romans 14 and Galatians 4 show that when people start treating days and seasons as a way to earn approval, they’re sliding back into slavery, not walking in the freedom He already bought.
These things are not a condition of your salvation, nor for keeping it, not needed since the cross because your standing with God is settled at the cross, not on a calendar.