tl;dr: Great advice in the many other comments. My $0.02 is to accept that for the most part, your colleagues are as interested in you as are your friends, and are as safe an audience. They are listening because you have experience and knowledge and perspective they do not, they want to be informed.

Making that mental/emotional switch from considering your colleagues as potentially questioning or hostile to accepting them as collegial and helpful can remove at least some of the anxiety that degrades one's self confidence.

Slightly longer version....

One major difference between speaking with friends and addressing colleagues or strangers is how we, the speaker, perceive the situation: We often perceive the latter differently and have different expectations, and these expectations can make us anxious.

Friends are generally supportive, we want to hear them and they want to hear us, because we are friends. Ribbing and personal needling aside. :->

We expect when speaking with friends that they will be receptive and relatively less judgemental. We are confident and engaged and engaging because we believe we are accepted and that our thoughts are wanted, appreciated.

Then we talk to colleagues or strangers and we feel the stakes are different, we feel they might challenge us and/or our ideas, might question us, might put us on the spot.

Yes, that can happen. Be prepared for it. When it happens, take a breath, take a moment, ask the person to clarify or expand on what they are saying. If they go ad hominem, suggest that the conversation remain focused on the topic. Patience and a few deep breaths can help navigate these situations, when they occur.

Which is, IMHO, rare. Be prepared for it, but do not expect it as the norm. Have those tools (patience, focus on the topic, asking questions) ready, but don't get them out before you begin!

If you can make that mental and emotional switch, you will generally feel more confident, because you will feel less like you and your ideas are about to be challenged or rejected.

Keep things conversational, appear and be thoughtful, try to state the key point(s) succinctly, then offer details only if people engage. If they don't, take things off line.

Heck, you can even suggest doing just that, e.g., to keep a meeting on track and focused: "I've got a concern with that approach, should we discuss it now, or take it offline?"

That does several things: 1) It gives you time to gather your thoughts and prepare that summary; 2) It gives you the appearance of being respectful of the meeting and of other's time (it's not about you and your ideas, it's about keeping things on track, only drilling down if there is consensus) - and it's not just appearance, you are being respectful in fact; 3) it gives others an opportunity to indicate that they may also have concerns and provides a forum - the off-line/after-the-fact conversation - to air and address those concerns.

The other thing that helped me be heard and helped me make my point was to change in my overall approach. I am a very enthusiastic person, even in my 50s, but I am often calmly enthusiastic, if you will.

That's a big change from 30 years ago, where I was so eager to share and to make my point that it was off-putting for others.

The more measured and respectful you seem, the more people will value your opinions and seek them out.

Finally, something super simple: Make notes. When you are saying "I have a concern, should we discuss it now or take it offline", jot down a couple of words or phrases that will jog your memory if you lose your train of thought.

(Ever watch a standup comedian get distracted and lose their train of thought while interacting with an audience? It's amazing: They are literally 100% exposed, people are expecting them to continue, and the train has exploded, because someone said something unexpected and unexpectedly funny. They take the time. They take a deep breath. Sometimes they even admit to being distracted and they use the same tricks the rest of us do: "Where was I? Oh, yes, Mom's wonky foot....")