iPad Pro Gen 2 10.5 constantly rebooting after updating from 13.3.1 to 13.4.1.

YES! I can corroborate that the current iPadOS 14 Beta update APPEARS TO FIX the 3-minute boot loop issue. As I write, I've had several hours without problems on Public Beta 3, which is the only one so far to fix the issue. As said by others, make sure you get Beta 3 to test whether it fixes this issue for you. (On my first go at this I was (automatically) given Beta 2, and was only offered the OTA update to Beta 3 the next day.)

TL;DR:

Opinions: (1) Some people posting on this forum seem to have different and/or additional symptoms to the original poster, and the majority including me (symptoms summarised below). So if this fix doesn't work for you it probably means that you have a different underlying problem that needs a different solution. (2) While I'm glad this seems fixed for now, the whole thing leaves a bad taste. Final word from Apple support at every turn has been, 'this is a hardware issue: pay £$500+ for repair'. This fix proves (if we needed proof) that iPadOSes 13.4.1 - 13.6 contained a 'bug' that unnecessarily bricked some relatively recent, top of the range (once), previously fully functional iPads FOR 2 MONTHS. There did not appear to be a mechanism for affected users to get a fair and timely resolution, so some (many?) paid for repairs or new devices. (I relied on my personal iPad for work and my employer paid for a replacement, fortunately just a week ago and so eligible for 'open-box' return.) My opinion of Apple would only be (mostly) restored if I see the bug acknowledged in 'patch notes', and hear that people affected get repair and replacement costs refunded on request. I get that affected users were 'a drop in the ocean', but the fact we've been vindicated (it's a firmware 'bug' not (just?) a 'hardware issue') shows that Apple needs a better procedure for this type of situation. Otherwise, they're accepting that some customers are going to get screwed, and they're fine with it.

Symptoms: immediately after updating to iPadOS 13.4.1 (and I assume any firmware 13.4.1 - 13.6), my iPad Pro Gen 2 10.5 reboots to Apple logo 3 minutes after sign in leaving the following in Settings>Privacy>Data Analytics: 2 x "stacks+thermalmonitord...ips" followed by "panic-full...ips" "no successful checkins from com.apple.thermalmonitord in 180 seconds..."

Timeline & attempts to fix: I upgrade to 13.4.1 on/around 10 May; posted in this forum on 19 May; had a tech support chat session in mid-May; emailed customer relations (as suggested by MichelPM) in May; had a Genius Bar appointment on 19 July (when I finally got back to London). I lost count of the number of DFU restores and iPadOS upgrades through 13.6 - none of which fixed the issue.