Yes, pressing power to shutdown will show up exactly like that - sounds like everything is fine, otherwise

Sounds like a failing battery, you would need a working battery to check/repair. Make sure to get the right battery for your model. Ifixit has a guide for battery replacement here - again not sure the exact model: JBL Boombox Battery Replacement It may be enough for you to get at the battery and check the numbers so you can get the right replacement. Hope this helps

Step 4 of this ifixit guide shows how to remove the stand: HP All-in-one PC Model 24 Motherboard Replacement (The method can vary depending on the exact model)

Looks like KB is part of the topcase in this series - so replace the topcase. Open the back and take a look - everything gets transplanted to the new topcase. Also, might want to check for any other signs of corrosion/liquid damage, while its open.

I would try this: Make sure laptop is powered off - if its on, hold down power button until it shuts off. Then to verify screen is working I would try the Lenovo LCD Self Test: "Use the following steps to run the LCD Self-Test: Turn off the computer. Connect the AC power adapter. Press Fn, left Ctrl, and the power button at the same time. ... The test lasts for about 20 seconds and then the computer turns off automatically, or press the power button to exit the test." It just shows the 5 single colours on screen. Black, white, red, green, blue. If that works, then the screen is ok. Turn it on again: Do you hear/see any activity? Fanspin, lights etc. Turn it off again, if needed by again holding in the power button until it shuts off, if needed. Try power refresh - unplug, hold power button for >30 seconds, then see if it turns on by pressing power button. If not, can try full power refresh, that involves opening the back and disconnecting the battery, then holding power button in for >30seconds Lenovo YOGA...

Looks like that is an NVMe M.2 2280 on the right lower part of the picture and right next to it (on the left) is an empty slot for a 2nd drive of the same type: https://guide-images.cdn.ifixit.com/igi/3uZOPMe3UQ2j2C... Have to look up prices more locally to where you are. Its a fairly straightforward operation, so yes, taking due care its easy. When installed, if you run Windows then open up Disk Management and make sure it shows up, format it/assign drive letter if needed/as you like, then you'll have the extra space available in Explorer. All the best, welcome to ifixit!

Here's what I would probably do: Check if the drive is recognised in BIOS, first. If so, then: get a thumb drive, install Ventoy https://www.ventoy.net/ on it, add Hiren's Boot CD (HBCD) iso to the drive, insert it into computer and boot to the thumbdrive, then boot HBCD. Now you will need somewhere to copy/backup the data to, have that prepared - another USB drive for e.g., plug that in and copy the data from the problem drive to the backup drive. HBCD has programs to help with this, e.g unstoppable copier is one I like, there are several already installed on there, if you don't use cmd/robocopy. Hope that helps!

SMART hard disk check failed? If so, further use could make things worse! I would stop trying to boot it. If you need the data, you will likely need to do data recovery on the drive. It may be you will need help of local PC shop for this, or not. Even if data is not required, the drive will need to be removed and replaced. If the removed drive is in good enough condition a clone to the new drive will work and OS and data will be preserved, best case scenario (provided new drive is at least the capacity of the old). Worst case, everything is lost on the drive, you will need to go through reinstalling OS/Apps etc on the new drive once you have it installed. To get the data from the failed drive would need advanced data recovery, which is not cheap! There are lot of variables with drive failures! If you want to try cloning/basic data recovery, let us know and we can try and guide you, but if not then a computer repair shop should be able to help you further. If going the new drive/reinstall everything route...

Depends on cause of the failure. Try booting and hitting F2 to get into diagnostics, check drive. If there was a Windows update that included a BIOS update - this may have reset BIOS options such as UEFI - try booting to BIOS by hitting F10, and see if boot options are UEFI or Legacy - if UEFI, try changing to legacy - save and restart - if it boots ok that was the issue. That model came with a HDD or SSD or possibly a HDD/SSD hybrid drive. Hybrid drive - depends on which part failed. If it was the SSD then you may be able to remove it and see if laptop works without it, as data would be on the HDD. If not, HDD may have failed. If drive has failed and you want to retain data vs a fresh install? Retain data, clone to new 2.5" SSD of same or larger capacity - I usually do this in another machine where I can connect the old and new drives and clone using clone software. If fresh install - create Windows USB installer, install new drive and boot (F9) to the Windows USB.

We need some more information: how many blinks, short or long? This link might help work out what the blink code means: https://support.hp.com/id-en/document/ish_1997719-1528356-16