Do I need to show 20,000 baht when passing through Thai immigration?

No not at all. I think it's a rule they keep just incase they need a reason not to let someone in

No one cares

No

Yes

No

In 22 extended vacations over the past 24 years, sometimes with a visa and some on walkin visa exemptions, I have never ben as to show cash or onward tickets. But that doesn't mean they can't or won't ask.

My cash is in USD not Thai Baht.

Does anyone know if cash can be in any currency or if it must be in Thai Baht?

No...

None needed but ATMs charge an arm and a leg.

No .. but inalways use the ATM machine in the airport anyway and with draw 20,000 baht without conversion

Never been asked in 15 years 3 times a year.

yes

No. I have been visiting Thailand annually for the past 20 years and have never carried any cash. Never asked for it.

That's the official immigration policy but in multiple entries over many years I have never once been asked about funds or anything else.

Officially you need it but they rarely ask. Same with an exit ticket out of Thailand, which you should have.

It's a law from 5 decades ago. An immigrations officer thinking he can still use it today has a bigger problem at the end of his (then last) working they than you. Can you imagine the headlines if one person got refused for having money in the bank?

It actually happened a year or so ago. They Thais started an investigation about what actually happened. It was clearly toned towards the immigrations officer's decisions being under scrutiny, not the fact that someone held money in the bank. The investigation concluded by the way the the claims were false and that the person in question was not refused entry, i.e. also not for having money in the bank. She was just a sensation seeking YouTuber. The statement dismissed the requirement as "secondary". But in the end, the headlines and media outrage that I imagined also before the incident, it was actually there ;)

If you are dressed like a homeless person, that would be a good idea. If you’re not, you should be OK.

99.9% they won’t ask for any money to be shown unless you have an extensive history in Thailand and they want a reason to deny you entry.

The chance of being asked,

is minimum.

but the decisions is up to the Immigrations officers.

Yes just incase you get asked

That's only a requirement if you're entering as a tourist, and it's only asked to show if they are looking for a reason to deny you entry. So if you've spent a large amount of time in Thailand already or made many entries, then it's a good idea to have it. Otherwise it's not something 99.999% of people need to worry about.