I recently bought a Thunderbolt 3 monitor as what I have vowed is my 'Last Thunderbolt 3 purchase (except replacing broken things)'.
I'm holding out for Thunderbolt 4, when I can (hopefully) treat my wiring topology like USB instead of daisy chained all to hell and back. Because of this, I looked at good qualities in a secondary monitor that were survivable on a primary. For instance sound quality and real estate are less important, raising the priority of PPI, color gamut, and VESA mount.
I'm holding out for Thunderbolt 4, when I can (hopefully) treat my wiring topology like USB instead of daisy chained all to hell and back. Because of this, I looked at good qualities in a secondary monitor that were survivable on a primary. For instance sound quality and real estate are less important, raising the priority of PPI, color gamut, and VESA mount.