I have no experience with a retirement visa in Cambodia, but my friends tell me that it is quite easy to get.
Concerning banks, I got my bank accounts more than 10 years ago. It was easy to get an account at that time, and I opened accounts in 7 different banks.
There have been no problems with the banks but currently, I only have 4 remaining banks. All my accounts are in US$.
1. ABA https://www.ababank.com/
is the most popular bank among my friends (local and expats) in Cambodia. The bank covers all types of bank business and is probably the most progressive all-round bank with a good reputation. It is a subsidiary of the National Bank of Canada.
2. KB Prasac (my favorite) https://www.kbprasacbank.com.kh/en/
Excellent for fixed accounts and plain bank accounts. Transferring to other Cambodian banks is free and instant, using the Bakong transfer system.
The bank is owned by KB Kookmin Bank, one of South Korea's biggest banks.
They give at the moment 8,25% on 12 months fixed accounts.
3. Hattha Bank https://hatthabank.com/
Hattha Bank is a subsidiary of the Thai Bank Krungsri.
Krungsri is a strategic member of the Mitsubishi UFJ Financial Group (MUFG), Japan’s largest financial group.
You can get 8% on a 12-month fixed account, and they have a money-on-demand account called HYSA account where you can get up to 5%
4. May Bank https://www.maybank2u.com.kh/
Malaysia's biggest bank.
I use that as a 'safe haven' and for transfer to and from Cambodia.
All the above banks use Bakong, https://bakong.nbc.gov.kh/en/ is a very excellent, free, domestic money transfer system.
There is a 14% tax on interest for foreigners, deducted before the interest is added to your account.
Where to live?
Well, I started in Phnom Penh but got tired of the traffic and chaos. 5 years ago I bought an apartment in Siem Reap. It is much smaller but has a big expat community and lots of exciting restaurants. It is probably Cambodia's most international city.
I like Thailand, but I love Cambodia.