Any omnipotent (occasionally benevolent) being has an array of secret weapons they can deploy at will to bend the universe to their whims.  DMs and GMs are no different.

In my campaigns, I employ a secret weapon I call "the red herring roll." I am 100% sure that I am not the only one doing this.  If I find that my players are losing focus, or I feel like I need to add an element of uncertainty or suspense, I will pick up any die (doesn't matter which) and roll it.  I look at the result, say "hmmm" and continue with the narrative. If my players ask "What was that?" I will ask for a check (perception of whatever is situationally appropriate).  I treat it as a DC 15, and if they make it I can make something up, or ask them for another roll and pull something off of a random encounter table, otherwise "You look around and see nothing." or "You feel (insert basic emotion here)."  I have found this add an element of anticipation and excitement.

Example: my players were traveling between towns and I would randomly roll now and then. Sometimes I would continue the narrative as planned, <roll> "it's a bright, sunny day with a light breeze.  You hear birds chirping and forest creatures in the distance." (Which is what I was going to say anyway). They go along, I roll randomly again and am asked "Do I see something?" I glance over at my random encounter table on my DM screen and see a prompt about a small circle of stones.  "You see a small circle of stones about 10 feet in diameter, near the treeline, about 50 yards away from the road." Immediately all my players are engaged, asking questions about the circle, can they make a history or nature check, etc.  "It's an old Druid circle, and you can see that it hasn't been used in a very long time." A few questions later they move one and we continue down the road.  All of the players are now focused on the narrative, have engaged in RP conversation amongst themselves, and have "bought into" the session.

Red herring dice rolls.  (One of) My secret weapons.  What are yours?

I used to do pretty much the same on in-person sessions. Now, with online sessions it does not work preety much that way, so I just forgo the "suspense roll" and the perception check. I go upright to some random non-hostile encounter like a nature feature or historic site as much as you do.

When I have no one that make a good match at the situation, I just make up a conversation between a warlock patron or a cleric deity, or just trhows up "You look the fields ahead and get stuck with images of (dramatic moment from backstory) in your head. The rest of you see's (that character) stop a bit and stare to nothing, like something is going on." Then they go into a nice drama or a long cat and mouse situation trying to convince that char to say more about him/her self.

Well, and also: "lets take a 5min break to fill the mugs and come back". We usually play sessions no longer than 4 hours or 4:30h so mostly that moment of getting lost with the engagement is around the middle of the session, but when I feel that something is not going to exitable for the players I just ask a second break, maybe even 3. Playing in person was way different than that but online sessions demand us to make that leg-stretching break more often.

I often use this red herring. Nothing trigger a player's suspicions ou questionings more than a myterious d20 roll they're asked to make without further justification or result given. :)

I'm using that red herring roll. My secret weapon is creating encounters that mess with the specific personalities of each character. I currently have an edgy half elf bard, a goliath with severe culture shock (He wouldn't pick a clan name so I dubbed him Marblehead,) and a lunatic rogue. I don't have the goliath's ready yet, but the bard is going to get slipped a philter of love, and the rogue will suffer a curse which will turn his body to gold and transfer his psyche to a cup, temporarily. (Seriously though, the rogue, both the player and the character, are insane. In Dragonheist there's a bar on the docks with an anchor in a roof. On a whim, I decided that the structural integrity of the building depended on the anchor being there. The rogue, having succeeded on the Investigation check, asked if he could pull out the anchor and shoot the patrons as they fled. There wasn't any combat necessary. Luckily for me, the idea was quickly shot down by the rest of the party.)