MySQL 8.0

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CREATE TABLE test (val VARCHAR(255) CHARACTER SET UTF8MB3 COLLATE utf8mb3_general_ci);
INSERT INTO test VALUES ('asdf'), ('фыва');
SHOW CREATE TABLE test;
SELECT val, HEX(val) FROM test;

Records: 2  Duplicates: 0  Warnings: 0

Table
Create Table

test
CREATE TABLE `test` (
  `val` varchar(255) CHARACTER SET utf8mb3 COLLATE utf8mb3_general_ci DEFAULT NULL
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_0900_ai_ci

val
HEX(val)

asdf
61736466

фыва
D184D18BD0B2D0B0

ALTER TABLE test
  MODIFY COLUMN val VARCHAR(255) CHARACTER SET latin1;

Incorrect string value: '\xD1\x84\xD1\x8B\xD0\xB2...' for column 'val' at row 2

ALTER TABLE test 
  MODIFY COLUMN val VARCHAR(255) CHARACTER SET UTF8MB4 COLLATE utf8mb4_general_ci;
SHOW CREATE TABLE test;
SELECT val, HEX(val) FROM test;

Records: 0  Duplicates: 0  Warnings: 0

Table
Create Table

test
CREATE TABLE `test` (
  `val` varchar(255) CHARACTER SET utf8mb4 COLLATE utf8mb4_general_ci DEFAULT NULL
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_0900_ai_ci

val
HEX(val)

asdf
61736466

фыва
D184D18BD0B2D0B0