HTML fields display with HTML Tags when exported and rendered in Excel format from List view:
1) Navigate to any list view which has an HTML Field.
2) Right Click on the headers
3) Export > Excel (.xlsx)
4) Observe the rows content after downloaded into the Excel file.
This ability to hide HTML Tags is currently not a part of the product.
Use Visual Basic Editor in Excel to clean the exported content.
The code to change a column from HTML to plain text can be something like this:
Dim cell As Range
Dim s As String
Dim asWd() As String
Dim iWd As Long
For Each cell In Intersect(Selection.Cells, ActiveSheet.UsedRange)
s = Replace(cell.Value, Chr(160), " ")
s = Replace(s, ">", "<")
s = Replace(s, vbCr, vbLf)
asWd = Split(s, "<")
s = vbNullString
For iWd = 0 To UBound(asWd) Step 2
s = s & " " & asWd(iWd)
Do While InStr(s, vbLf & " ")
s = Replace(s, vbLf & " ", vbLf)
Do While InStr(s, vbLf & vbLf)
s = Replace(s, vbLf & vbLf, vbLf)
cell.Value = WorksheetFunction.Trim(s)
See more extensive details and instructions in the community post Rendering HTML in Exported Lists.
Documentation pages: List export.