I'm currently using GrapheneOS and I quite like it, but I would like to switch to something else. Will I lose much privacy if I switch to e/OS? Can I lock bootloader after flashing it like on GrapheneOS? I'm using Pixel 7 btw
you'll definitely be loosing security, which can turn into loosing privacy if you get affected by malware.
you'll also be loosing privacy if installing proprietary apps, since GrapheneOS has features like storage scopes and a better permission system that help minimizing privacy issues.
I think that locking your bootloader in a Pixel is possible regardless of the ROM you install.
Anyway, I think that there's no real benefit of installing any other custom ROM in a Pixel other than GrapheneOS. You'll be just loosing out in security and potentially privacy for no real reason.
I recommend sticking to GOS. If you'd like to use something else, I'd recommend DivestOS. CalyxOS, LineageOS, /e/OS and iodéOS are all significant downgrades in usability, privacy and security and therefore not worth using on a Pixel.