Unfortunately, there’s no alternative to a GrapheneOS phone nowadays.

• Linux phones: good privacy and good customization, but poor security, poor hardware support and poorish software support (e.g. android apps that require play verification)
• iOS: good security, almost okayish privacy, but you basically don’t own your phone
• Mainline Android: good compatibility, good hardware support, but poor to abysmal (depending on the make) security, poor to abysmal privacy, you almost don’t own your phone
• Lineage OS / iodeOS / etc: goodish privacy, adequate support for a lot of hardware, control over your phone, but poorish security, poorish software support (e.g. android apps that require play verification), lack of hardware support (e.g. the very S21)
• Fairphone & similar — they fall somewhere in the middle between mainline Android and LineageOS stuff — better privacy than mainline, more flexibility than mainline, but still dependency on Google whims, and poorish security.

That said, IMO there are two directions:

• Pixel phone (or Motorola in the future) + GrapheneOS — good software but new meh hardware —
• Current phone, maximally decrapped (ideally, almost everything but very core services disabled, e.g. via universal debloater or manually via adb) — much more private than mainline Android, relatively stable and with at least some baseline security + critical security patches from the OEM