You can be an atheist and give stuff up for Lent, okay. It’s not even unusual.
I find it weird when people find the two things incompatible. Maybe that’s because I went to a Catholic school where practically everybody observed Lent regardless of what they believed, but like… no. It’s not unusual. I’m not appropriating, it’s okay to fast without being religious.
Lent isn’t even obligatory for Christians, and an atheist can still get most of the benefits that a Christian will out of a fast. I find it awesome and humbling to be so aware that I have so much, and I can choose to give something up for Lent. I think it’s good to be reminded of how privileged you are no matter what. Hmm.