So apparently crossplay has been enabled for PS4 since around

Borderlands 3 cross-play update won't come to PS4 and PS5

PlayStation 4 - Wikipedia

Fall Guys' mid-season update adds 2 new rounds and cross-play on

Console Players Will Need to Learn How to Shoot as Overwatch 2

Final Fantasy XIV Heading to Xbox, Cross-Play Supported - Siliconera

Epic vs. Apple court documents reveal why Sony was against cross

Edifier G2II Gaming Headset for PC PS4 USB Wired

Sony charges for crossplay support to protect PSN revenue

When should games be developed for multiple platforms? When

Best crossplay games: play with friends across platforms

Disabled Gamers Raise Concerns Over Decision to Scrap PS4 Pads on

Sony PlayStation Responds to Backlash Over PS4 Crossplay

Sony apparently won't allow Ark: Survival Evolved PS4-Xbox One

What does Warframe's next-gen cross-save and crossplay mean for PC

The Ascent Update Actually Disables Cross-Play Between PS5 and PS4