Usually fine
SUM, SUMIF/SUMIFS, COUNTIF, AVERAGE, IF, AND/OR, VLOOKUP, INDEX/MATCH, IFERROR, TEXT, LEFT/RIGHT/MID, DATE, EOMONTH, ROUND, PMT, NPV on vanilla workbooks. Named ranges that are simple. Charts that are not 3D explosions.
Test before you promise
XLOOKUP, FILTER, UNIQUE, SORT, SEQUENCE, and LET/LAMBDA are Microsoft 365-era tools. Some WPS builds implement parts; some return errors. Make a 20-row sample, open it in both suites, and screenshot the difference before you tell a client it is compatible.
Array habits that punish both suites
Formulas on entire columns, volatile OFFSET/INDIRECT forests, and conditional formats on a million rows will crawl in WPS and Excel. Switch to manual calc (F9). Use the 64-bit desktop build. Save locally while you recalc. Performance notes.
Pivot tables
Basic pivots often survive. Slicers, Power Query, Power Pivot, and data models are Excel’s house. If the workbook is a Power Query machine, do not migrate it as a hobby project.
Macros
Let one suite own XLSM. Open read-only in the other. Security: do not enable macros from email just because WPS asked. Safety.
CSV
CSV is not a formatted report. Dates and leading zeros die. For interchange, agree UTF-8 and a date format. For a dashboard, stay in XLSX.