"Hey, I never liked Office 365, Microsoft as a company and all the Cloud shenanigans... And have you noticed how their products all become shittier and more invasive by the day? All while they increase subscription price each year now to finance all the AI stuff I rarely use? I'm a long-term fan of this other product, called XYZ which is just better in every aspect. No offense. If you want me to send you a link..."

(Edit: It'll become easier after a while. At some point they all know you're a Linux nerd and disassembled your wifi router at home, dishwasher... To get rid of proprietary spy components. And people will deliberately decide to listen to your opinion and lengthy rant, or make an effort to not bring up the topic 😆 At that point, you're relatively free to speak your mind... Just read the room a bit. The goal isn't to annoy people.)