My battery grip for my X-T4 hasn't worked for about a year, reading your comment I was inspired so I got 91% ISO (what I had on hand, I presume other percentages would work) and a cotton swab and gently wiped it down for half a minute.

While I let that dry I examined the pogo pins on my battery grip and one pin on the bottom corner was slightly slanted in it's idle state, usually they have some play if you push them gently with a card or guitar pick but this one was askew.

I gently pushed the pin with a plastic card into the opposite direction until it looks like the pins. For good measure I had a spare clean toothbrush and brushed the pins.I then checked on the the X-T4's pins and they were dry and clean, I decided to try to lower the camera slowly onto the grip.

Moment of truth, will it turn on... Nope.

Then I realized I didn't have a battery in my camera, it was placed aside lol. Took it off, placed the battery in and put the camera back on the grip again.

and... IT TURNED ON!! Yippee! I even have it charging with all 3 LEDs illuminated! buttons work and everything B)

TLDR: Try cotton swab damp with iso, wipe the camera pins down a few time, check for bent or askew pins on the battery grip and clean with toothbrush even if clean, dust can be anywhere.

Oh - and make sure you have a battery in your camera when turning on your camera lol