Hello, achow101
thanks for your reply.

I just copy and paste btc-wallet.dat to the directory where located default wallet.dat and blocks folder, then select it from drawdown list in the bitcoin-core ui.
I did not change the default configuration after installing bitcoin core and blocks synchronization, therefore my bitcoin.conf file from the same directory with wallet.dat, btc-wallet.dat, blocks folder is empty.
Please take a look the image: https://ibb.co/BNsJyg8

Hello, everyone!

  Please help in my weird situation :

I had some amount of satoshi/bitcoin in spring 2018 (all blocks took ~140Gb).
Ballance was correct in bitcoin-core ui (v. 0.16), I encrypted and backed up the btc-wallet.dat. Its size 1328 kb.
Today (15 of November 2020) I removed all blocks, reinstalled bitcoin-core (v. 0.20), and re-synchronized all blocks (took ~333Gb).
After synchronization, I have default wallet.dat in the root directory, its size 1448 kb.

When I choose to use another pasted to the root wallet - btc-wallet.dat, then bitcoin-core starts rescanning (needed ~90mins):
2020-11-15T22:31:31Z init message: Rescanning ...
2020-11-15T22:31:31Z [btc-wallet.dat] Rescanning last 282497 blocks (from block 374599)...
2020-11-15T22:31:31Z [btc-wallet.dat] Rescan started from block 0000000000000000005fb267cc42dc8630668db3cd1f6a484374fbb4a5ccfc22...
2020-11-15T22:32:31Z [btc-wallet.dat] Still rescanning. At block 507124. Progress=0.509806
...
2020-11-15T23:54:31Z [btc-wallet.dat] Still rescanning. At block 655890. Progress=0.996076
2020-11-15T23:55:19Z [btc-wallet.dat] Rescan completed in         5027754ms
2020-11-15T23:55:19Z [btc-wallet.dat] setKeyPool.size() = 2000
2020-11-15T23:55:19Z [btc-wallet.dat] mapWallet.size() = 0
2020-11-15T23:55:19Z [btc-wallet.dat] m_address_book.size() = 1

When rescan is finished, the size of btc-wallet.dat becomes 1056 kB and the wallet has 0 balance without in/out-coming in 2018 transactions . Looks like this file (btc-wallet.dat) was overwritten by the bitcoin-core .

What I'm doing wrong and how to fix/return/read my funds.

I will be appreciated for any help, thanks in advance.