[Google Pixel 5a] fjm568:
Apologies...long rambling post ahead...

Truthfully, I don't remember exactly how I got it to switch slots or if that eventually enabled me to factory reset and sideload the latest OTA.

Ok...thinking about it a little bit...

I noticed that after trying to sideload latest OTA, during the reboot, when the G logo first comes up, it looked different, basically a color change in the logo that I'd never noticed before. I figured that meant it was trying to restart the new OTA. Then, if I'm remembering correctly, the screen would go black and then the old G logo reappeared and went into boot loop from there.

As I said in my previous post, I really don't recommend this, and try it at your own expense...Don't blame me if it bricks your phone. My first recommendation is to try to get it fixed under warranty if you can.

Read this through to the end before you try it.

Now, here's the sketchy part...if you still want to try this...While the phone was in the first restart after sideloading latest OTA while the G logo looked different, I forced(power and vol down) the phone to go back to the bootloader menu. When I got into the fastboot mode screen, where it shows the phone info, if your bootloader is locked or unlocked, and what slot you are currently in, etc., at that point, my phone was showing I was in slot b, where before it was slot a. At that point, I went back to the bootloader menu and I did the factory reset, and the phone restarted normally. After that, I don't remember if I unlocked the bootloader at that point, or if I side loaded the latest OTA, and then unlocked my bootloader.

Don't wait too long after the first reboot try after the latest OTA attempt to try to get it to the bootloader screen while it's in the other slot. Once it reboots again, it's back in the old slot and bootloops.

I think that is the way that I did it. It worked on my first try, dumb luck I guess. Again, try at your own risk. I figured I didn't have anything to lose. My next step if it didn't work was to try the warranty repair.

Here's how I got the idea. I wanted to see what OTA version was installed when the G logo changed. I think that before I did the factory reset, but after I forced it into the fastboot mode screen, I noticed I was in a different slot than normal. I then tried to let it start normal, and then after it started bootlooping, I again restarted it into the fastboot mode screen and it was then I noticed it was back in the normal slot(bootlooping). That's when I got the idea, to again force it to the other slot, and THEN factory reset.

On a side note, my phone seems to be working fine now and has done the latest OTA update normally.

Good luck, hope it works for you. Don't be mad at me if it bricks your phone. I am a noob, never went to school for this stuff, and fumble my way through this tech stuff with help from people here a lot smarter at this stuff than me.

If it doesn't work for you, and still goes into bootloops, maybe try again but adjust when you try to force it to go to the bootloader menu.

edit...

I just checked...When I attempted this fix, I was bootlooping in slot a...I forced it to slot b, factory reset, sideloaded latest OTA, restarted and eventually accepted the current March update, and it now shows I am in slot a.

Hopefully, you can make some sense of how I did it, and I didn't confuse you. If you have any questions, ask, and I'll try to answer. Reply with a quote of one of my posts, so I'll get notified, and I'll try to answer promptly.

Again...Good luck.