Selling of shares, capital gains / payouts from investment / crypto portfolios may be tax-exempt (the so-called 3-year rule).
Dividends from portfolios are not tax-exempt.
ETF / Trading. Trading is subject to taxes.
Capital gains from trades under 100.000 CZK, but not exempt by the 3-year rule, still do not have to be declared in the Tax Return.
Foreign taxes may have been deducted from investments, but Czech taxes still apply.
Investment losses can not be carried forward to the next year or applied to other paragraphs in the tax return.
Profit on Czech property sales is tax-exempt following the 3-year rule or if the profits are used for own housing needs.
Sporadic other income from Czech Republic or abroad: if it your only source of income and it is less than 50.000 CZK, no tax return needs to be filed.
Foreign self-employment, business profits may fit in §7 or §10 - depending whether you have a CZ trade license and whether the foreign business is (considered) sole proprietorship (file in §7 with active CZ TL) or an independent legal entity with a dividend payout (usually file in §10).